Why don't we move Spire's Module/VectorSpace/MetricSpace/etc. here?

[ctongfei]

I think that these typeclasses should go into Algebra.

[johnynek]

I think we could do this. Would you be interested in opening a PR starting at the bottom of that hierarchy?

[ctongfei]

Thanks :-) I'd be happy to do that.

[denisrosset]

@ctongfei Beware!

I'm currently revising the Spire test suite. The Spire hierarchy has a few inconsistencies; for example, Module pretends to be noncommutative, but actually it is defined in a way that only makes sense for commutative rings. MetricSpace/InnerProductSpace/CoordinateSpace are only valid when the vector spaces are defined on the reals, ...