This makes the regular expression a bit more complex, and potentially
slower, but it will fix the issue where users had noqa comments with
colons followed by explanations.

Closes #178

Fix read_lines_splits_lines test for CRLF endings

This change makes the test pass for when files are saved with CRLF Windows-style line endings since those are included in various `.readlines()` methods by default.

See merge request !96

We accidentally changed column numbering from one-indexed to
zero-indexed.

Flake8 3.0 was stopping once it found the current directory but the
historical behaviour (that we didn't intend to break) searched past
that (towards root) until it found one of the project/local config
file names that could be read.

Closes #181

This allows for other text after `# noqa`.

Related to #180

It is possible to write plugins which are only a function. At the moment they
are called on each line manually. This allows the function also to be called
on each file once. It works similar to creating the class and calling `run` on
it immediately. The plugin function needs to return a generator.

This is based on the original comment in the `FileChecker.run_ast_checks`
method, but slightly modified as the original comment would've called the
return of the function. But the function could return the reports directly.

This simplifies the changes, reduces the scope of refactors apparently
for refactoring's sake and ensures that the internals are reasonable.

It also airs on the side of preserving information rather than
discarding or overwriting it.

This way plugins like flake8-putty can have access to the correct filename.