More type classes

[Fresheyeball]

I ended up writing this for myself, but against the 0.6.x psc. The version here is for 0.7 psc, which I have not tested, but should be fine.

[garyb]

This won't quite work, as the operators for Semiring, ModuloSemiring and Ring have been renamed in 0.7 (to named functions, but the operators will still be available as aliases). Also the purescript-foldable-traversable dependency already pulls in purescript-monoid and purescript-invariant.

Thanks though 😉 I'll update it with the classes you added here.

[Fresheyeball]

Ok, is reasonable.