Normalize include guards for all *.h and *.hpp

Some files had include guards that didn't match the file name, and
others were missing the include guards entirely.

Standardized this so that every include file has an include guard, and
all the guards are of the form TWOBLUECUBES_<FILENAME>_<EXT>_INCLUDED

include/internal/catch_impl.hpp

@@ -5,6 +5,8 @@
  *  Distributed under the Boost Software License, Version 1.0. (See accompanying
  *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  */
+#ifndef TWOBLUECUBES_CATCH_IMPL_HPP_INCLUDED
+#define TWOBLUECUBES_CATCH_IMPL_HPP_INCLUDED
 
 // Collect all the implementation files together here
 // These are the equivalent of what would usually be cpp files
@@ -65,3 +67,5 @@ namespace Catch {
 #ifdef __clang__
 #pragma clang diagnostic pop
 #endif
+
+#endif // TWOBLUECUBES_CATCH_IMPL_HPP_INCLUDED