fix(checker): allow whitespace before inner functions and class

[johanfleury]

Changes D202: ("No blank lines allowed after function docstring") to
allow space below function docstrings with inner functions.

i.e. allows:

def outer():
    """Valid docstring."""

    def inner():
        pass

    return pass

See comment from @cdeil in #361.

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This is a follow-up of PR #395.

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• Add unit tests and integration tests where applicable.
  If you've added an error code or changed an error code behavior,
  you should probably add or change a test case file under tests/test_cases/ and add
  it to the list under tests/test_definitions.py.
  If you've added or changed a command line option,
  you should probably add or change a test in tests/test_integration.py.
• Add a line to the release notes (docs/release_notes.rst) under "Current Development Version".
  Make sure to include the PR number after you open and get one.

[Code0x58]

I just thought, there is the case of decorators around classes/functions, so that regex and test file could use @ cases.

For example it's fairly common to write a decorator that uses functions.wraps(...)

[johanfleury]

I updated the PR and also added a commit to fix some DeprecationWarning.

[Code0x58]

Great!

[ColinKennedy]

I just stumbled upon this PR. Is there anything that I can do to help it along or is it ready to merge?

[johanfleury]

@ColinKennedy we're just waiting for a review by a project member.

[Nurdok]

Sorry for the long delays in response - I've been on back-to-back family vacation and business trips. I'll to catch up as soon as I can.