pg_chameleon 2.0.15

The new maintenance release for pg_chameleon adds the support for reduced lock if MySQL engine is transactional, thanks to [rascalDan](https://github.com/rascalDan)

The initialisation process now checks whether the engine for the table is transactional and runs the initial copy within a transaction.
The process still requires a FLUSH TABLES WITH READ LOCK but the lock is released as soon as the transaction snapshot is acquired.
This improvement allows pg\_chameleon to run against primary databases with minimal impact during the init\_replica process.

The python-mysql-replication requirement is now changed to version >=0.22 which adds the support for PyMySQL >=0.10.0.