[Library] pawn-plus-mysql: PawnPlus extensions and helpers for the MySQL plugin

[kristo]

I know pawn-plus uses this naming scheme, but please don't copy it. One thing we want to do with open.mp is promote consistency in naming schemes and styles. The argument used with pawn-plus was that the core library is inconsistent, so why can't that also be inconsistent (in a different way)? We intend to fix the core library.

Actually I think it follows the naming scheme of the MySQL plugin.