Darglint2

Changed

- Renamed the project to `darglint2` while forking it from the archived
[terrencepreilly/darglint](https://github.com/terrencepreilly/darglint) to
[akaihola/darglint2](https://github.com/terrencepreilly/darglint2).

Added

- There is now a Flake8 flag exposing the ignore regex option. This will
allow you to ignore a given file/set of files based on a regex during
a CI pipeline, etc. Thanks to AdamGleave for the pull request!

Changed

- Removed logging for some aspects of analysis, and an assertion from the
raise visitor. They were a little overly-broad, and it was causing some
integration tests to fail when run against new repos.

Added

- We now ignore return, pass, yield, and raise in abstract methods.
Thanks to maltevesper!

Fixed

- Resolved most of the mypy issues in the repository. This is mostly a
code cleanliness issue.

Added

- We now recognize property methods on a class, and there are options to ignore
properties for checking. Thanks to saroad2!

Added

- Added an option to ignore the presence of certain exceptions. This is
useful if your project has a common error which you don't want to have to
document everywhere (for example, a custom assertion error.) This can be
used through the `ignore_raise` configuration option, or command-line option.
Thanks to palt0 for the pull request!
- Added `ignore_regex` as a command-line option (this already existed as a
configuration option, but I overlooked it as a command-line option.) Thanks
to saroad2 for the pull request!

Changed

- Deprecated Python3.5 support, since it breaks the Travis CI build. I've left
the dockerfile test for it in, as everything still works.
- Added Python3.9 support.

Fixed

- Changed *config.cfg* to *setup.cfg* in the pre-commit documentation, which was
the correct name. Thanks to nuno-andre for the pull request.
- Load the `enable` option from the configuration file, so that disabled-by-default
errors can be shown. Thanks to palt0 for the pull request!

Fixed

- Bare returns now do not have to be documented. This aligns better with
expectations for docstrings, and matches what darglint did prior to refactoring
to handle nested functions.