chore: Adopt src/ layout and tox

[effigies]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.35%. Comparing base (e2f720d) to head (f911418).
Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #458      +/-   ##
==========================================
+ Coverage   66.76%   74.35%   +7.59%     
==========================================
  Files          31       25       -6     
  Lines        2079     1938     -141     
  Branches      205      240      +35     
==========================================
+ Hits         1388     1441      +53     
+ Misses        691      432     -259     
- Partials        0       65      +65     

Flag	Coverage Δ
ds054	45.79% <ø> (?)

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[effigies]

@mgxd if you could have a look, I'd appreciate it.

[mgxd]

Looks really good - one question since it's not clear to me whether its present:

Do we still compare the tag version with the built version of the package? I found that check useful for catching mislabeled and dirty releases

[effigies]

The tests for the docker image are still there on Circle, which is where we've had actual problems AFAIR. Building the wheels for PyPI is generally less problematic, since you clone the whole repo and there isn't anything like .dockerignore to get in the way.