Added violation for multiline loops

[Ben-Drebing]

I have made things!

Implemented the MultiLineLoopViolation which is produced when the "iterator" section of a for-loop and the "test" section of a while-loop take up multiple lines.

Checklist

• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made
• I have added my changes to the CHANGELOG.md

Related issues

Closes #813

[sobolevn]

Thanks a lot! Great job! Just two minor comments and we are ready to go!

[Ben-Drebing]

Should be all good to go now! You might have noticed I remembered to run flake8 this time :)

[sobolevn]

@Ben-Drebing can you please fix this issue?

$ make test
mypy wemake_python_styleguide
wemake_python_styleguide/visitors/ast/loops.py:196: error: Argument 1 to "add_violation" of "BaseVisitor" has incompatible type "Type[MultilineLoopViolation]"; expected "BaseViolation"
Found 1 error in 1 file (checked 102 source files)

[coveralls]

Pull Request Test Coverage Report for Build 2071

• 15 of 15 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 2067:	0.0%
Covered Lines:	4765
Relevant Lines:	4765

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💛 - Coveralls