Cats-effect: Proposal (2) 😀 cats-concurrent project, top level or sub-project of cats-effect

[alexandru]

I'm thinking that people need concurrency data types that use cats-effect type classes, but that we don't necessarily want to push in cats-effect in order to preserve the stability of the project,
being a big believer in an a la carte approach.

I'm currently thinking of:

1. some Scheduler data type as outlined in #116 - now i'm thinking of renaming that to Timer 😀
2. MVar
3. Ref

Could be in the same repository, as a sub-project. Or it could be a new top-level Typelevel project.

[johnynek]

I think it should be a subproject of cats-effect. Many repos creates a lot of difficulty in publishing when new incompatible versions comes.

I think concurrent is so close to effect s submodule is very natural.

[alexandru]

When I opened this issue, I was thinking of Timer, which ended up in cats-effect proper.

I think if we add a concurrent sub-project to cats-effect it will have the same stability requirements as cats-effect. Which actually isn't bad at all. So for now I'm abandoning such plans for a separate project. If something is truly needed, it probably belongs to cats-effect.