Add TextFeatureMapper, hardcoded for Duga's Programmer-comments features

src/main/java/net/zomis/machlearn/text/TextFeatureMapper.java

@@ -0,0 +1,20 @@
+package net.zomis.machlearn.text;
+
+import java.util.stream.IntStream;
+
+public class TextFeatureMapper {
+
+    private static final String[] CONTAINS = {
+        "better fit", "better suited", "better place",
+        "close", "off-topic", "design", "whiteboard", "this question", "this site",
+        "programmers.se", "help at", "place to ask", "migrate", "belong",
+        "instead", "the place for", "try programmers", "for programmers",
+        "on programmers", "at programmers", "to programmers" };
+
+    public double[] toFeatures(String str) {
+        return IntStream.range(0, CONTAINS.length)
+            .mapToDouble(i -> str.contains(CONTAINS[i]) ? 1 : 0)
+            .toArray();
+    }
+
+}