Composite primary keys (gobuffalo#47)

* WIP composite primary keys

* Add tests for t.PrimaryKey()

* Add composite primary key support in translators

* Fix remaining issues

* Add doc about composite primary key

* Change primaryKey field name to primaryKeys

This way it matches the getter name.

Bump version

Bump version

Version bump

version bump: v1.5.0

Bump version

Bump version

Bump version

Add MariaDB support (gobuffalo#25)

* Add MariaDB support

* Add missing files

Support float precision fixes gobuffalo#8 (gobuffalo#36)

* Support float precision fixes gobuffalo#8

* Fix fixmie issues

* Fix bad comment formatting