Add Cofree.ana and Cofree.anaEval

[andyscott]

Adds Cofree.ana (update: added anaEval too), which generalizes Cofree.unfold with a fused map. The map fused version is a bit more useful than the basic unfold, especially when you're unfolding from some other messy structure.

I stuck with the name from the Haskell category extras package but I suppose unfoldMap (or mapUnfold?) might also be a good name for this.

[codecov-io]

Codecov Report

Merging #2325 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2325      +/-   ##
==========================================
+ Coverage   95.07%   95.08%   +<.01%     
==========================================
  Files         343      343              
  Lines        5931     5935       +4     
  Branches      217      216       -1     
==========================================
+ Hits         5639     5643       +4     
  Misses        292      292

Impacted Files	Coverage Δ
free/src/main/scala/cats/free/Cofree.scala	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 186dbab...a545438. Read the comment docs.

[johnynek]

Looks great!

[LukaJCB]

Looks good to me 👍

About naming, I think ana is a good name personally, but anaE is a bit strange, we have a bunch of functions that use Eval as a postfix, like map2Eval or productREval so maybe it's appropriate here too? :)

[andyscott]

Seems reasonable to me. I'll unfold E to Eval 😄.

[andyscott]

The build seems to have freaked out-- possibly related to GitHub being down briefly. I don't have permissions to restart it so maybe someone here could?

[tpolecat]

done

[LukaJCB]

Ready to merge @andyscott? :)

[andyscott]

Yes, definitely 🤘