Fix precommit regex (and format / linter errors)

[DropD]

In .pre-commit-config.yaml:

• the file: regex were reformatted to the style documented at http://pre-commit.com/#regular-expressions
• since every sub-expression in the regex must now match the full path, folders were extended to match path/to/folder/.*.py
• The format was documented with comments where such a regex first occurs
• hook versions were updated using pre-commit autoupdate

Other changes:

• all other changes are formatting and linter fixes that previously weren't caught by pre-comit run --all-files

fix #860

[ltalirz]

Thanks Rico!
I'm not sure whether regular expressions are really needed here, but if it's the best way of splitting the string that's fine. In some corner cases one might have unintended consequences when one isn't careful (e.g. some of the dots in your example are not escaped). But it's fine with me.

There is one issue, namely the

- repo: git://github.com/pre-commit/pre-commit-hooks
  sha: v1.1.1
  hooks:
  - id: check-yaml

leads to the following error on my conda installation

$ git commit -a
[INFO] Installing environment for git://github.com/pre-commit/pre-commit-hooks.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
An unexpected error has occurred: CalledProcessError: Command: ('/Users/leopold/Applications/miniconda3/bin/python', '-m', 'virtualenv', '/Users/leopold/.cache/pre-commit/repo0z0cpahk/py_env-python3.6', '-p', 'python3.6')
Return code: 100
Expected return code: 0
Output:
    Using base prefix '/Users/leopold/Applications/miniconda3'
    New python executable in /Users/leopold/.cache/pre-commit/repo0z0cpahk/py_env-python3.6/bin/python3.6
    Also creating executable in /Users/leopold/.cache/pre-commit/repo0z0cpahk/py_env-python3.6/bin/python
    ERROR: The executable /Users/leopold/.cache/pre-commit/repo0z0cpahk/py_env-python3.6/bin/python3.6 is not functioning
    ERROR: It thinks sys.prefix is '/' (should be '/Users/leopold/.cache/pre-commit/repo0z0cpahk/py_env-python3.6')
    ERROR: virtualenv is not compatible with this system or executable
    Running virtualenv with interpreter /Users/leopold/Applications/miniconda3/bin/python3.6

Errors:
    dyld: Library not loaded: @rpath/libpython3.6m.dylib
      Referenced from: /Users/leopold/.cache/pre-commit/repo0z0cpahk/py_env-python3.6/bin/python3.6
      Reason: image not found

I searched for it a bit yesterday and didn't find the solution.
Not sure whether you have an idea for a solution. Otherwise, I'll simply have to comment this block out on my machine.

[ltalirz]

In case you want to push it: from my point of view using regex is not ideal, but fine.
Otherwise, feel free to wait for @szoupanos

[szoupanos]

The check seems to find my modified files now. Thanks!