Make matched route accessible via Request

[falbrechtskirchinger]

Resolves #2101.

[urosg80]

just my thoughts but I think it would be more inline with the structure to use std::string instead of char* as there is no other pointer used in either Request or Response struct and if we would want to for the library to be more memory efficient then the whole library should move away from C++ types and move to C types; inserting one char* instead of std::string doesn't really accomplish anything IMHO.