Move basic typeclasses into cats-kernel

[rklaehn]

Cats will lose the dependency on algebra. In order for algebra and spire to depend on cats, there needs to be a small and stable core of essential typeclasses (algebra and spire will not want to depend on all of cats).

This core should contain at least

Eq
Order/PartialOrder
Semigroup/Monoid/Group
Show

I think it would be OK to have the core not that small, since the main concern from the algebra side is not .jar size but binary compatibility concerns. So if it is an advantage to have e.g. SemigroupK and MonoidK in there as well, that would be fine IMHO.

@non maybe just having all of algebra depend on cats-core is also acceptable. The only thing I really want to avoid is having duplicated typeclasses in cats and algebra.

[rklaehn]

here is a proof of concept for a library that uses simulacrum to generate typeclass boilerplate, but does not have it in the .pom
https://github.com/rklaehn/hash

Here is how to hide simulacrum from the .pom (in case "provided" is not good enough):
rklaehn/hash@2f11a6c

[ceedubs]

This was resolved with #1001.