Move CI tests to GitHub actions

[patrick91]

This should make it easier to test under multiple python versions (ie 3.8 beta)

[botberry]

Thanks for adding the RELEASE.md file!

Here's a preview of the changelog:

---

Tests are now run on GitHub actions on both python 3.7 and python3.8 🐍

[patrick91]

This is blocked by GitHub not having beta python versions :( actions/setup-python#15

[marcoacierno]

Can we merge it if it works and then update it once Github supports 3.8?

[patrick91]

@marcoacierno I think we should try to add 3.8a on Circle CI and then when it is supported on GH Actions we can migrate :)

[codecov]

Codecov Report

Merging #148 into master will increase coverage by 4.71%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
+ Coverage   90.66%   95.38%   +4.71%     
==========================================
  Files          23       54      +31     
  Lines         493     1755    +1262     
==========================================
+ Hits          447     1674    +1227     
- Misses         46       81      +35

[patrick91]

This can be merged when uvloop 0.14 gets released (as it is broken on py38)