v1.0.0-M2

Changelog:

• further improvements to Cats' instances for Chimney types - added Alternative type class to the list of provided instances, a few missed discipline tests were added (#465)
• provided a flag to disable automatic Option unwrapping by PartialTransformer (#322, addressed by #477) (disabling that behavior by default is not planned)

This pre-release is the second from the planned series of internal cleanups. The series is intended to make sure that when 1.0.0 is finally released it will not have any serious (known) issues that could be only addressed by breaking the backward compatibility. We will be really glad if you tested it, and let us know about any such issues while they are still easy to fix.