Run code from Python files

[hermansje]

Executing Python files on the file system opens up a lot more SCT capabilities.
Function chain to use this: check_file().run().has_equal_value()
There are some tests showing how it can be used.

[codecov]

Codecov Report

Merging #381 into master will decrease coverage by 0.52%.
The diff coverage is 90.6%.

@@            Coverage Diff             @@
##           master     #381      +/-   ##
==========================================
- Coverage    94.6%   94.08%   -0.53%     
==========================================
  Files          26       26              
  Lines        1984     2097     +113     
==========================================
+ Hits         1877     1973      +96     
- Misses        107      124      +17

Impacted Files	Coverage Δ
pythonwhat/checks/has_funcs.py	96.17% <100%> (ø)	⬆️
pythonwhat/checks/check_wrappers.py	100% <100%> (ø)	⬆️
pythonwhat/State.py	93.42% <100%> (-1.14%)	⬇️
pythonwhat/sct_syntax.py	100% <100%> (ø)	⬆️
pythonwhat/test_exercise.py	97.5% <100%> (+0.53%)	⬆️
pythonwhat/checks/check_object.py	100% <100%> (ø)	⬆️
pythonwhat/local.py	89.28% <88.8%> (-10.72%)	⬇️

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