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.

include/internal/catch_matchers_string.h

@@ -8,8 +8,6 @@
 #ifndef TWOBLUECUBES_CATCH_MATCHERS_STRING_H_INCLUDED
 #define TWOBLUECUBES_CATCH_MATCHERS_STRING_H_INCLUDED
 
-#if !defined(CATCH_CONFIG_DISABLE_MATCHERS)
-
 #include "catch_matchers.hpp"
 
 #include <string>
@@ -68,6 +66,4 @@ namespace Matchers {
 } // namespace Matchers
 } // namespace Catch
 
-#endif // CATCH_CONFIG_DISABLE_MATCHERS
-
 #endif // TWOBLUECUBES_CATCH_MATCHERS_STRING_H_INCLUDED