PEP8 Fixes

This PR bundles a lot of formatting changes to make the codebase more PEP8-compliant. The nature of the modifications makes this a rather heavy pull request: after applying the changes mentioned below, the total size of the repository dropped a total of 0.5M (from 6.7M to 6.2M). In addition, the changes also reduce the amount of PEP8 errors/warnings from 3763 errors/warnings to 1854 errors/warnings.

In more detail: this pull request resolves all* generated PEP8 warnings and errors except for:
* **E111** indentation is not a multiple of four
* **E121** continuation line indentation is not a multiple of four
* **E122** continuation line missing indentation or outdented
* **E123** closing bracket does not match indentation of opening bracket’s line
* **E124** closing bracket does not match visual indentation
* **E125** continuation line does not distinguish itself from next logical line
* **E126** continuation line over-indented for hanging indent
* **E127** continuation line over-indented for visual indent
* **E128** continuation line under-indented for visual indent
* **E501** line too long (82 > 79 characters)
* **E711** comparison to None should be ‘if cond is None:’
    - E711 in particular causes some tests to fail.

\* By all, I mean all Python files except for `BeautifulSoup.py` and anything in `httplib2/`.

There is only one commit in this set that is not related to PEP8 (384d57efa59665f0dd47c07062a8177a2eedde9a) - that replaces a print statement in `run_tests.py` with a warning. I forgot that I still had that on the branch and was too lazy to rebase/perform git trickery.

All unit tests pass, but that doesn't mean that I or [autopep8](https://github.com/hhatto/autopep8) didn't do something wrong.