Introduce and run pre-commit

[Mojken]

No description provided.

[Swamii]

Great 👍

[Mojken]

This is what flake8 complained about btw:

runtests.py:15:20: C408 Unnecessary dict call - rewrite as a literal.
DEFAULT_SETTINGS = dict(
                   ^
djedi/__init__.py:36:14: C408 Unnecessary dict call - rewrite as a literal.
    config = dict(
             ^
djedi/admin/__init__.py:20:17: C408 Unnecessary dict call - rewrite as a literal.
                dict(
                ^
docs/conf.py:185:5: E265 block comment should start with '# '
    #'papersize': 'letterpaper',
    ^
docs/conf.py:187:5: E265 block comment should start with '# '
    #'pointsize': '10pt',
    ^
docs/conf.py:189:5: E265 block comment should start with '# '
    #'preamble': '',
    ^
djedi/compat.py:99:1: E402 module level import not at top of file
from collections import namedtuple
^
djedi/compat.py:100:1: E402 module level import not at top of file
from inspect import getfullargspec
^

[Mojken]

Closing in favor of #93