Bump the version string as well

Create sub-sections for different release series

When looking at the documentation, the release notes section on the
sidebar was incredibly long, due to the number of releases available.
To make this more usable, I've split the release notes index into
sections for each release series (e.g., 3.x, 2.x, etc.). This allows
documentation users to open the release notes sidebar section, and then
select which series they want. That will expand and let them pick the
version.

See merge request !145

Document Flake8 for users expecting `man flake8` to work and include the
man page in Flake8's documentation.

Closes #247

When looking at the documentation, the release notes section on the
sidebar was incredibly long, due to the number of releases available.
To make this more usable, I've split the release notes index into
sections for each release series (e.g., 3.x, 2.x, etc.). This allows
documentation users to open the release notes sidebar section, and then
select which series they want. That will expand and let them pick the
version.

Add documentation for VCS hooks

Closes #249

See merge request !144

Closes #249

This section of the docs could be read as pointing out the project as a
bad example. It was not intended this way, but I would like to avoid
anyone interpreting it this way. As a result, we'll continue to use
their configuration section as an example but not name names.

Closes #228

If we handle an exception, or early exit, or really anything, we should
exit non-zero (and we used to). This was a minor oversight.

Closes #209
Closes #248