Moves all the error checking to the free functions.

This is done so that there are two simple parts to our mysql wrapping:

1. Wrap all mysql-c-api functions in error-checking versions.
2. Wrap those functions in a nice OOP-layer with a Connection, UseResult and a Statement
   The OOP-layer doesn't have to do any error checking, since that's already done in point
   1.
Merge branch 'version-2' of github.com:Wassasin/librusql into version-2

Conflicts:
	src/rusql/rumysql.hpp
	Upstream created UseResult::field_seek, removed that, created rusql::mysql::field_seek in mysql_error_checked.