Add bindings for mysql_{library,thread}_{init,end} functions

This allows clients to fix potential memory leaks discussed in http://sourceforge.net/p/mysql-python/bugs/177/

mysql_thread_end() is the important thing, but this change goes ahead and modernizes the docstrings and bindings for mysql_server_init/mysql_server_end to note that the mysql_server_* names are deprecated and offer mysql_library_* versions.