Use iostream instead of C-style file operations.
Use InspIRCd::Format instead of snprintf().
Replace some C string operations with the + operator.
Rewrite irc::sockets::sockaddrs::str() completely.

- Replace use of MAXBUF with INET_ADDRSTRLEN/INET6_ADDRSTRLEN.
- Replace use of sprintf with InspIRCd::Format.
Convert ConvNumeric() to use std::string instead of char[MAXBUF].
Convert User::FormatNoticeMasks() to use std::string.
Convert User::SendText to use std::string.
Convert a ton of uses of MAXBUF to use a fixed buffer size.
Remove hardcoded MAXBUF constant.