clean up dependencies, py2 code, etc 🚿

[lindsay-stevens]

Closes #558

Why is this the best possible solution? Were any other approaches considered?

This PR includes a range of janitorial changes intended to make maintenance easier:

• separate the prod code and dependencies from those for test / dev
  • remove test code and files from the pip install pyxform package (wheel/sdist)
  • update setup.cfg so that:
  • the wheel package isn't marked as py2-compatible
  • all the linters / formatters agree on 90 character lines
  • update test / dev dependencies to latest versions
  • resulted in numerous formatting changes due to black update
  • move tests into separate tests root folder so it's easier to grep / search code
  • tests and tests_v1 merged into one folder because they're all relevant
  • modules using old-style XFormTestCase put in xform_test_case sub-folder
  • update CI dotfiles accordingly for the above changes
• remove some of the more obvious py2 compatibility remnants, such as:
  • imports from __future__, conditional imports, usage of unicodecsv and unittest2
  • aliasing from unicode or basestring to str, and unichr to chr
• resolve numerous code style errors and warnings from flake8, pycodestyle, pycharm
  • includes removing chunk of cascading-select code that was already broken (571962d)
• update the README to reflect current dev setup process and testing guidelines

What are the regression risks?

Pyxform v1.0.0 (2020-02-06) removed Python 2 compatibility, but due to a lot of compatibility stuff being left in place it's possible that some are still using Pyxform on py2. This PR makes it almost certain that Pyxform will not work on py2.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

As mentioned above, the README was updated where relevant. No changes needed to user XLSForm docs.

Before submitting this PR, please make sure you have:

• [x] included test cases for core behavior and edge cases in tests_v1
• [x] run nosetests and verified all tests pass
• [x] run black pyxform to format code
• [x] verified that any code or assets from external sources are properly credited in comments

[codecov-commenter]

Codecov Report

Merging #562 (f46afd3) into master (94af8bc) will increase coverage by 0.86%. The diff coverage is 84.74%.

@@            Coverage Diff             @@
##           master     #562      +/-   ##
==========================================
+ Coverage   83.36%   84.22%   +0.86%     
==========================================
  Files          25       25              
  Lines        3738     3665      -73     
  Branches      875      863      -12     
==========================================
- Hits         3116     3087      -29     
+ Misses        482      439      -43     
+ Partials      140      139       -1     

Impacted Files	Coverage Δ
pyxform/validators/enketo_validate/__init__.py	34.21% <ø> (ø)
pyxform/xls2xform.py	81.57% <ø> (-0.24%)	:arrow_down:
pyxform/xform2json.py	79.37% <45.45%> (-0.05%)	:arrow_down:
pyxform/survey_element.py	94.40% <60.00%> (+0.32%)	:arrow_up:
pyxform/xform_instance_parser.py	71.91% <66.66%> (-0.32%)	:arrow_down:
pyxform/validators/updater.py	83.00% <80.00%> (-0.12%)	:arrow_down:
pyxform/xls2json.py	79.49% <85.18%> (+3.17%)	:arrow_up:
pyxform/utils.py	91.33% <88.88%> (+5.02%)	:arrow_up:
pyxform/xls2json_backends.py	76.33% <88.88%> (-0.14%)	:arrow_down:
pyxform/builder.py	77.07% <100.00%> (-0.12%)	:arrow_down:
... and 10 more

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[lognaturel]

Have taken a quick look and don't see any issues. 👍 I'm hoping it will be a quick rebase on master to fix conflicts. I'll finish the review today or tomorrow.

[lindsay-stevens]

resolved merge conflicts

[lindsay-stevens]

Great, thanks @lognaturel !

About the tests and blame, the moves were tracked (git mv) so they should still show up in blame. At least, they do for me - both on CLI and GitHub when browsing the PR branch. One exception being 1750d59 where I copied the XFormTestCase definition lines into a different file. But we can still go to the parent commit and blame from there if needed.

About the conflict PRs, I agree it would be simpler to proceed with this PR and resolve conflicts in other PRs; than to try to resolve them first then incorporate into this PR.

About squashing, I don't mind either way. Many of the commits are noisy but some have potentially useful context.

[lognaturel]

they do for me - both on CLI and GitHub when browsing the PR branch

That's excellent! I didn't try here, I've had trouble with Github following moves in the past but maybe either the way you did it or changes on Github's side made this better. Either way, fantastic!

Many of the commits are noisy but some have potentially useful context.

I don't find them noisy and I'd tend to want to keep them but I think they'd be hard to use because some strange things happened in merges and rebases and they are all duplicated. My experience is also that it's hard to navigate history through multiple layers of merge commits. Seems like it will be most useful in the long term to squash and refer back to this PR if more context is needed. I don't think there's a quick way to get a clean history with just the desired commits.