Migrate to CircleCI

[AdamGleave]

• Add CircleCI Config
• Delete .travis.yml config
• Add Dockerfile and build image, with MuJoCo support
• Parallelize tests using pytest-shard.

Should run significantly faster now.

No longer testing 3.6 so I've dropped support from that in setup.py. I don't feel strongly about this so we could also just test in 3.6 instead of 3.7. However I feel OK with only officially supporting latest release (3.8) plus last one.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@43e23fa). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #121   +/-   ##
=========================================
  Coverage          ?   84.35%           
=========================================
  Files             ?       58           
  Lines             ?     3932           
  Branches          ?        0           
=========================================
  Hits              ?     3317           
  Misses            ?      615           
  Partials          ?        0

Impacted Files	Coverage Δ
src/imitation/scripts/parallel.py	93.54% <100%> (ø)
src/imitation/scripts/config/parallel.py	63.46% <100%> (ø)
src/imitation/testing/envs.py	100% <100%> (ø)
tests/test_scripts.py	100% <100%> (ø)

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[shwang]

Thanks for the patch. Here's a few nits and some questions about how the new system works:

[shwang]

Wow, 4min only for tests! (Used to be almost 20min per job)

[shwang]

LGTM

[shwang]

updated README instructions to match setup.py (supports python 3.8 and 3.7)