replace char array pointer with string container

this should fix issue #7
added more log messages regarding the charset
improved threading system

The execution of MySQL functions (like Connect, SetCharset, ...) has now a higher priority than the execution of queries.  This fixes a bug where the charset was applied after the execution of a query, even though mysql_set_charset was called before mysql_tquery from within the PAWN script. The only exception is the Disconnect function, which is only called after all queries have been sent and executed.