Adding ping()

MySQL connection will go away when idle timeout. The ping() function
can confirm the connectivity and also reconnect if need.
https://dev.mysql.com/doc/refman/5.7/en/mysql-ping.html
Thanks @joecharlier.

Allowing batch queries.

3.0.1

Allowing batch query.

Upgrading to Swift 4.0

3.0.0

Update readme to Swift 4.0

All tests passed on OS X

Please check the README file for a proper configuration of PC file.

MariaDB library build for Perfect

Only tested on macOS X