Implement set and list comprehension

[JSAbrahams]

Relevant issues

• Resolves #415

Summary

Implement set and list builder.

Both in generate and check stage. First condition is assumed to be a set.

Added Tests

Happy

• Set builder.
• List builder.
• Set/list builder with multiple conditions.
• Nested list comprehensions, to check if environment properly propagates out variables.

Sad

• Empty conditions in set builder.
• Undefined variables in conditions.
• Conditions which do not all evaluate to a boolean.

[codecov[bot]]

Codecov Report

Merging #418 (719f739) into develop (337760a) will increase coverage by 0.48%. The diff coverage is 89.13%.

@@             Coverage Diff             @@
##           develop     #418      +/-   ##
===========================================
+ Coverage    87.52%   88.01%   +0.48%     
===========================================
  Files          109      110       +1     
  Lines        12020    12079      +59     
===========================================
+ Hits         10521    10631     +110     
+ Misses        1499     1448      -51     

Impacted Files	Coverage Δ
src/generate/ast/node.rs	77.86% <0.00%> (-0.60%)	:arrow_down:
src/generate/convert/builder.rs	75.00% <75.00%> (ø)
src/check/ident.rs	96.38% <83.33%> (+0.04%)	:arrow_up:
src/check/constrain/generate/collection.rs	96.80% <100.00%> (+14.99%)	:arrow_up:
src/check/constrain/generate/operation.rs	94.61% <100.00%> (+2.80%)	:arrow_up:
src/generate/ast/mod.rs	95.10% <100.00%> (+0.58%)	:arrow_up:
src/generate/convert/mod.rs	94.78% <100.00%> (+0.96%)	:arrow_up:
src/check/context/python.rs	65.00% <0.00%> (-11.32%)	:arrow_down:
src/check/context/clss/python.rs	86.95% <0.00%> (-0.09%)	:arrow_down:
... and 9 more