Switched exception constants to const char * const (from const std::string) so we don't have to construct them all in every translation unit, and switched the exception class to derive from std::runtime_error (so it handles what() for us)

src/exp.cpp

@@ -107,7 +107,7 @@ namespace YAML
 			}
 
 			std::stringstream msg;
-			throw ParserException(in.mark(), ErrorMsg::INVALID_ESCAPE + ch);
+			throw ParserException(in.mark(), std::string(ErrorMsg::INVALID_ESCAPE) + ch);
 		}
 	}
 }