Cleanup and write tests for clifford.cga

[eric-wieser]

This doesn't attempt to fix any bugs, but at least converts unknown bugs into known bugs. The bugs this exposed are:

• Fix silly mistake in Flat constructor #100
• cga.Flat.__repr__ crashes with AttributeError #180
• cga.Dilation(mv) crashes with TypeError #181
• cga.Transversion(mv).mv != mv #182
• cga.Round.radius is always 1 #184
• cga.Rotation does not roundtrip rotations of 90n degrees #185

[codecov]

Codecov Report

Merging #183 into master will increase coverage by 2.82%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #183      +/-   ##
========================================
+ Coverage   52.17%    55%   +2.82%     
========================================
  Files          41     42       +1     
  Lines        6355   6419      +64     
  Branches      987    989       +2     
========================================
+ Hits         3316   3531     +215     
+ Misses       2913   2743     -170     
- Partials      126    145      +19

Impacted Files	Coverage Δ
clifford/cga.py	84.57% <100%> (+84.57%)	⬆️
clifford/test/test_cga.py	100% <100%> (ø)
clifford/tools/g3c/object_clustering.py	64.28% <0%> (-4.09%)	⬇️
clifford/test/test_g3c_tools.py	77.52% <0%> (-0.24%)	⬇️
clifford/_multivector.py	61.12% <0%> (+0.46%)	⬆️

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[eric-wieser]

Travis passes, coverage increased, and there are open issues for all the xfailing tests. If the tests seem like nonsense, we can fix them in a follow-up / discuss in the open bugs

[arsenovic]

nice job on this.