Fix inconsistent newlines read from a file in python3 (try 2)

Closes #457

See merge request pycqa/flake8!255

This reverts commit ba2fb9c5, reversing
changes made to 63b91c95.

Revert "Merge branch 'match_newlines_py3' into 'master'"

See merge request pycqa/flake8!254

This reverts merge request !253

Fix inconsistent newlines read from a file in python3

Closes #457

See merge request pycqa/flake8!253

Fix collections ABCs deprecation warning

See merge request pycqa/flake8!249

Signed-off-by: Jintao Zhang <zhangjintao9020@gmail.com>

Use black to reformat Flake8

See merge request pycqa/flake8!251

Instead of just using Flake8 and pylint to keep Flake8 clean, let's also
use black to make it less manual for clean-up.

Fix docs for --isolated flag

See merge request pycqa/flake8!247

Defer setuptools import to save ~60ms on startup

See merge request pycqa/flake8!250

(I ran this 5 times and picked a median result)

### before

```console
$ time flake8 --help > /dev/null

real    0m0.221s
user    0m0.199s
sys     0m0.020s
```

### after

```console
$ time flake8 --help > /dev/null

real    0m0.169s
user    0m0.144s
sys     0m0.020s
```

Only skip a file if `# flake8: noqa` is on a line by itself

See merge request pycqa/flake8!219

Update to pyflakes 2.0.0

Closes #422

See merge request pycqa/flake8!239

docs: Fix two typos

See merge request pycqa/flake8!236

Remove py33 from tox

See merge request pycqa/flake8!240

Update documentation links to latest Python 3 documentation

See merge request pycqa/flake8!242

Fix "styl" -> "style" typo in writing code docs

See merge request pycqa/flake8!243

Fix "invalid escape sequence" when running with -Werror

See merge request pycqa/flake8!244

```
$ python3.7 -Werror
Python 3.7.0rc1 (default, Jun 16 2018, 03:32:08) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> '# noqa(?:: (?P<codes>([A-Z][0-9]+(?:[,\s]+)?)+))?'
  File "<stdin>", line 1
SyntaxError: invalid escape sequence \s
```

The URL https://docs.python.org/3/ is actively maintained and updated.

- Add new pyflakes codes
- Bump the required versions
- Fixes https://gitlab.com/pycqa/flake8/issues/422

Got:

    flake8 requires Python '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
    but the running Python is 3.3.7

Add Python 3.7 to tox and GitLab CI

See merge request pycqa/flake8!234

docs: Link fixes and redirect avoidance

Closes #308

See merge request pycqa/flake8!235

        styl -> style
        commnts -> comments

Spelling and grammar fixes

See merge request pycqa/flake8!232

Implement --extend-ignore

See merge request pycqa/flake8!233

Refs #365