fix rendering of code samples in documentation

[larsks]

The code samples in the docstrings of the irc.connection module were not rendering properly in the generated output. This commit adds the necessary syntax so that they render as code.

[jaraco]

Thanks for the contrib. You may have noticed that the tests execute code in docstrings, and if that code doesn't execute cleanly, then the tests fail. That's why the tests for this PR are failing. There are a few options:

• suppress unrunnable tests with # +doctest:skip (or similar). Great for one line, but not great for a lot of tests
• update the code to actually be runnable
• disable the tests for this module in conftest.py or similar
• Instead of supplying as runnable code, use a different syntax for the code that displays as code but doesn't intend to run it.

I think I'd prefer (2) or (4), but I welcome you to explore the options.

[larsks]

I've rewritten the docs to use rst code-block directives. I think the amount of boilerplate necessary to make the code runnable would negatively impact the usefulness of the documentation.

[jaraco]

Fantastic! Thanks for the contrib.