Adding support for Phinx

[richmilns]

I have added support for Phinx and also had a bit of a refactor and tidy up.

I've only added support for MySQL/MariaDB with Phinx because I don't use PostgreSQL personally, but my code does support dumping index and foreign key definitions!

Version was bumped to 1.4b1, so that might need updating if you're happy and I also edited the README which you might want to ignore :)