Add linter for Python scripts

[yomcube]

Fixes #64.

[yomcube]

• TODO: search for files in the same way the clang-format job does

[vabold]

Can I get an explanation of what these options do?

[yomcube]

Outdated file, here's the new one:

[MESSAGES CONTROL]
disable=global-statement,
        import-error,
        invalid-name,
        missing-module-docstring,
        missing-class-docstring,
        missing-function-docstring,
        too-many-locals,
        too-many-return-statements,
        too-few-public-methods,
        fixme

[FORMAT]
max-line-length=100

• global-statement:

  Used when you use the "global" statement to update a global variable. Pylint discourages its usage. That doesn't mean you cannot use it!

  bot.py uses the global statement to access IS_GENERATING_KRKG and IS_REPLAYING_GHOST. I'm not sure what to use instead of globals, so I disabled this message. More here on why global variables are discoraged.
  Removed; messages can be shown without failing the action.

• import-error:

  ~~Used when pylint has been unable to import a module.

  Pylint can't import generate_tests, since it's a local module. See here for a potential fix.
  Removed; fixed by using init-hook in .pylintrc to append tools/ to the module path.

• invalid-name:

  Used when the name doesn't conform to naming rules associated to its type (constant, variable, class...).

  The checker thinks that local variables in a scope like a if __name__ == '__main__': block are global, so it flags them wrongly. Also flags camelCase variables (e.g. rkgPath), saying they should be snake_case.

• missing-(module|class|function)-docstring:

  Used when a module has no docstring. Empty modules do not require a docstring.

  Used when a class has no docstring. Even an empty class must have a docstring.

  Used when a function or method has no docstring. Some special methods like __init__ do not require a docstring.

  No documentation is necessary. (See #development on Discord)

• too-many-locals:

  Used when a function or method has too many local variables.

  Occurs in generate_tests in generate_tests.py. I didn't think this was a necessary message, since it's only one over the limit (16/15).

• too-many-return-statements:

  Used when a function or method has too many return statement, making it hard to follow.

  Occurs in KinokoOutputValidator.validate_test_case in status_check.py.
  Removed; messages can be shown without failing the action.

• too-few-public-methods:

  Used when class has too few public methods, so be sure it's really worth it.

  Occurs in the TestCase class in generate_tests.py. The class doesn't need any sort of methods, so I disabled this message.

• fixme:

  Used when a warning note as FIXME or XXX is detected.

  Also detects TODO comments, like in discord/bot.py (in command_generate_krkg and command_replay_ghost). I don't think it's necessary to fail the action from TODO comments, so I disabled this message.
  Removed; messages can be shown without failing the action.