Reorganise the standard library

[alcarney]

• It makes more sense to have everything related to a given "thing" to be located in the same place. So the shapes, patterns and operators modules have been merged into a single arlunio.lib.mask module.

  The parameters module has now also been renamed to math

• Updated the arlunio-image directive to align to the above change and also made it so that an error when rendering an image is also logged during a sphinx build

• Change virtualenv name from .dev to .env

• Fix reference to flake8 in the .pre-commit-config.yaml file

[codecov]

Codecov Report

Merging #227 into develop will decrease coverage by 0.04%.
The diff coverage is 92.85%.

@@             Coverage Diff             @@
##           develop     #227      +/-   ##
===========================================
- Coverage    73.75%   73.70%   -0.05%     
===========================================
  Files           17       18       +1     
  Lines          983      985       +2     
===========================================
+ Hits           725      726       +1     
- Misses         258      259       +1     

Flag	Coverage Δ
#unittests	73.70% <92.85%> (-0.05%)	⬇️

Impacted Files	Coverage Δ
arlunio/_core.py	95.81% <ø> (-0.02%)	⬇️
arlunio/lib/math.py	100.00% <ø> (ø)
arlunio/doc/directives.py	73.25% <77.77%> (-2.03%)	⬇️
arlunio/lib/mask/__init__.py	100.00% <100.00%> (ø)
arlunio/lib/mask/mask.py	72.72% <100.00%> (ø)
arlunio/lib/mask/pattern.py	31.42% <100.00%> (ø)
arlunio/lib/mask/shape.py	33.82% <100.00%> (ø)

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