Moved matcher-based capture macros into their own file

- this file excluded from the CATCH_CONFIG_DISABLE_MATCHERS path.
- matchers are always compiled in to the impl file
- _THROWS_WITH macros are still available with matchers disabled - but only the ones that take a string
- tests that use matchers have #ifdefs, so the whole SelfTest project can compile with matchers disable.

projects/SelfTest/TagAliasTests.cpp

@@ -11,8 +11,6 @@
 
 TEST_CASE( "Tag alias can be registered against tag patterns" ) {
 
-    using namespace Catch::Matchers;
-
     Catch::TagAliasRegistry registry;
 
     registry.add( "[@zzz]", "[one][two]", Catch::SourceLineInfo( "file", 2 ) );
@@ -24,11 +22,14 @@ TEST_CASE( "Tag alias can be registered against tag patterns" ) {
             FAIL( "expected exception" );
         }
         catch( std::exception& ex ) {
+#ifndef CATCH_CONFIG_DISABLE_MATCHERS
             std::string what = ex.what();
+            using namespace Catch::Matchers;
             CHECK_THAT( what, Contains( "[@zzz]" ) );
             CHECK_THAT( what, Contains( "file" ) );
             CHECK_THAT( what, Contains( "2" ) );
             CHECK_THAT( what, Contains( "10" ) );
+#endif
         }
     }