Add service and plugin type to process scripts

This will be useful for implementing script processing directives in
an extensible way. Here is one example, for dependency declaration:

  #@repository('https://maven.imagej.net/content/groups/public')
  #@dependency('net.imagej:imagej:2.0.0-rc-60')

And here is another, for defining the intended script language:

  #!clojure

We will also migrate the script parameter syntax to this scheme:

  #@input String name
  #@input int age
  #@output String greeting

Or with the familiar sloppy shorthand:

  #@string name
  #@int age
  #@output String greeting

See #265
See scijava/scijava-jupyter-kernel#51 (comment)

Author: ctrueden

src/main/java/org/scijava/script/DefaultScriptProcessorService.java

@@ -0,0 +1,49 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
+ * Institute of Molecular Cell Biology and Genetics.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.script;
+
+import org.scijava.plugin.AbstractSingletonService;
+import org.scijava.plugin.Plugin;
+import org.scijava.service.Service;
+
+/**
+ * Default implementation of {@link ScriptProcessorService}.
+ * 
+ * @author Curtis Rueden
+ */
+@Plugin(type = Service.class)
+public class DefaultScriptProcessorService extends
+	AbstractSingletonService<ScriptProcessor> implements
+	ScriptProcessorService
+{
+	// NB: No implementation needed.
+}

src/main/java/org/scijava/script/ScriptProcessor.java

@@ -0,0 +1,52 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
+ * Institute of Molecular Cell Biology and Genetics.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.script;
+
+import org.scijava.plugin.SingletonPlugin;
+
+/**
+ * A script processor defines some sort of processing that primes a particular
+ * script for execution.
+ * <p>
+ * Typically, these plugins look for special directives in the script itself
+ * beginning with distinctive character sequences like {@code #@}, and then
+ * perform some action in response.
+ * </p>
+ * 
+ * @author Curtis Rueden
+ */
+public interface ScriptProcessor extends SingletonPlugin {
+
+	/** Performs a processing step on the given script. */
+	void process(ScriptInfo info);
+
+}

src/main/java/org/scijava/script/ScriptProcessorService.java

@@ -0,0 +1,64 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
+ * Institute of Molecular Cell Biology and Genetics.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.script;
+
+import org.scijava.plugin.SingletonService;
+import org.scijava.service.SciJavaService;
+
+/**
+ * Interface for service that processes scripts. This service discovers
+ * available {@link ScriptProcessor} plugins, and provides convenience methods
+ * to interact with them.
+ * 
+ * @author Curtis Rueden
+ */
+public interface ScriptProcessorService extends
+	SingletonService<ScriptProcessor>, SciJavaService
+{
+
+	/**
+	 * Invokes all {@link ScriptProcessor} plugins on the given script, in
+	 * sequence.
+	 */
+	default void process(final ScriptInfo info) {
+		for (final ScriptProcessor p : getInstances()) {
+			p.process(info);
+		}
+	}
+
+	// -- PTService methods --
+
+	@Override
+	default Class<ScriptProcessor> getPluginType() {
+		return ScriptProcessor.class;
+	}
+}

src/test/java/org/scijava/ContextCreationTest.java

@@ -109,6 +109,7 @@ public void testFull() {
 				org.scijava.prefs.DefaultPrefService.class,
 				org.scijava.run.DefaultRunService.class,
 				org.scijava.script.DefaultScriptHeaderService.class,
+				org.scijava.script.DefaultScriptProcessorService.class,
 				org.scijava.text.DefaultTextService.class,
 				org.scijava.thread.DefaultThreadService.class,
 				org.scijava.tool.DefaultToolService.class,