allow configuration of default reporter

[robertlemmen]

setting the reporter on the cmdline is nice, but it would be good to be able to set the default one in the compilation. if only so that prove/prove6 can be used nicely, which seem to be unable to pass arguments to the thing under test....

--- /usr/include/catch.hpp      2017-08-01 15:10:43.564565422 +0100
+++ catch.hpp   2017-08-01 15:16:20.332581488 +0100
@@ -5630,9 +5630,14 @@
                 m_config->setStreamBuf( m_ofs.rdbuf() );
             }
         }
+
+#ifndef CATCH_CONFIG_DEFAULT_REPORTER
+#define CATCH_CONFIG_DEFAULT_REPORTER "console"
+#endif
+
         void makeReporter() {
             std::string reporterName = m_config->getReporterName().empty()
-                ? "console"
+                ? CATCH_CONFIG_DEFAULT_REPORTER
                 : m_config->getReporterName();
 
             m_reporter = getRegistryHub().getReporterRegistry().create( reporterName, m_config.get() );