v1.0.0-M3

Changelog:

• added a way to customize how source fields/subtypes are matches against target fields/subtypes (#89 and #480, fixed in #478) - thanks to @saeltz for contributing to the PR as the first contribution!

This pre-release is the third 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.