Move Free/State to data package?

[ceedubs]

Currently there are separate (but small) packages for free and state. This is because up until #760 they were in their own separate modules. Now that they are within core, should we drop the free/state from their package name and move them to the data package to be more consistent with other types like WriterT?

I'm not sure data is a particularly meaningful package name for some of these types, but that's probably a tangential issue (if it's an "issue" at all).

[dwijnand]

👍 from me, for either cats.data or cats.

[travisbrown]

👍, and I'm fine with having them all directly under cats.data.

[ceedubs]

Update: Since #990 was merged, this no longer applies to free.

[ceedubs]

Oops I just realized that State has already been moved to the data package. Looks like it's time to close this out.