Preliminary PR: ProMotion 1.2

Since the [discussion around ProMotion 2.0](https://github.com/clearsightstudio/ProMotion/issues/356) is taking ProMotion in a new direction, we'd like to release a version 1.2.

This release will include some features that were originally slated for PM 2.0; namely, use of `motion_require`.

This preliminary pull request does not address deprecations. I hope to add deprecation warnings soon, perhaps in a lighter 1.3 release.

From now on, `edge` will refer to 1.x releases and something like `pm2` will refer to the 2.0 branch.

I'll update this PR with a changelog shortly.