Scala 2.13.0-RC1 support

[rossabaker]

Fixes #507. Blocked by typelevel/cats#2783.

[rossabaker]

This is built on binary-incompatible cats-laws, and should be released as 2.0.0-M1 for the same reason.

[rossabaker]

I don't know that this is the best place for this. It replaces catalysts, and is only needed in tests.

[djspiewak]

The interesting thing here is this implies that cats-effect 2.0 is going to have roughly the same hierarchy and features as cats-effect 1.0, and so any major changes get pushed to 3.0. It's just a naming thing, but it's worth calling out.

[rossabaker]

Correct. It was an open question whether we'd break cats-effect-core in 2.0 with anything that's ready, or strictly follow cats' lead. My default stance is conservative here.

My stronger opinion is that a cats-effect-2.0 is needed quickly, compatible with cats-laws 2.0, and to deal with the eviction warnings that are about to plague us all.

[codecov-io]

Codecov Report

Merging #508 into master will decrease coverage by 4.24%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #508      +/-   ##
=========================================
- Coverage   89.95%   85.7%   -4.25%     
=========================================
  Files          70      70              
  Lines        2050    2148      +98     
  Branches      128     131       +3     
=========================================
- Hits         1844    1841       -3     
- Misses        206     307     +101

[rossabaker]

Build is now failing because the Java 11 install is repeatedly erring out on Travis CI.

[djspiewak]

Merged your xenial PR. I think that unblocks this?

[rossabaker]

Naughtily did a force push, since nobody had commented individual lines. I expect this build to be green.