Replace some C-isms with C++-isms.

* 'const char*' to 'const std::string&'.
* snprintf to std::string concatenation.
* Replace duplicated OneOfMatches with InspIRCd::MatchMask.
Merge pull request #531 from SaberUK/master+snprintf-removal

Replace some C-isms with C++-isms.
[WIP] Get rid of strlcpy(), strlcat(), charlcat() and charremove()