non/spire — pull request #277 by tixxit (2014-07-11 00:30:39+00:00)
Title: GroupAction for Sign and other bits

This does a few things:

* It adds a `MultiplicativeGroupAction` for `Sign`, so we can write expressions like `sign *> x`,
* Loosens the scalar member on `GroupAction` to only be a `Semigroup` instead of a `Group`,
* Adds convenience methods to switch between `Additive/MultiplicativeGroupAction` and `GroupAction`, and
* Adds `GroupActionLaws` and some property tests using it for `Sign`.