Modernize docstrings & make everything consistent

[dgw]

This whole initiative started with #1563, but I only dealt with one file in that PR.

The whole public API (at least) should get an overhaul before we release 7.0, to make sure the API docs are really nice and easy to use. We only use Sphinx magic like :param: descriptions in a few places so far, and it would be awesome to have those everywhere.

Here's the important (public) stuff:

• sopel.bot (bot, irc: doc overhaul #1772)
• sopel.cli (cli: modernize docstrings #1922)
  • Probably already modern given that @Exirel wrote it, but I'll still go @Exirel went through it again
  • Review/overhaul pushed to 7.1
• sopel.config (config: doc overhaul #1778)
  • sopel.config.core_section (config: doc overhaul #1778)
  • sopel.config.types (config.types: doc ALL the things! #1719)
• sopel.db (db, docs: overhaul docstrings & add SQLAlchemy to intersphinx mappings #1776)
• sopel.formatting (formatting: docstring overhaul #1766)
• sopel.irc (bot, irc: doc overhaul #1772)
  • sopel.irc.abstract_backends (bot, irc: doc overhaul #1772)
  • sopel.irc.backends (bot, irc: doc overhaul #1772)
  • sopel.irc.utils (bot, irc: doc overhaul #1772)
• sopel.logger (logger: doc overhaul #1775)
• sopel.module (module: docstring overhaul & modernization #1770)
• sopel.tools (tools: Overhaul docstrings #1563)
  • sopel.tools.calculation (tools: subpackage doc overhaul #1771)
  • sopel.tools.jobs (tools: subpackage doc overhaul #1771)
  • sopel.tools.target (tools: subpackage doc overhaul #1771)
  • sopel.tools.time (tools: subpackage doc overhaul #1771)
  • sopel.tools.web (moved from sopel.web in Transition web -> tools.web #1616; doc updates in Document tools.web package #1669)
• sopel.trigger (trigger: doc overhaul #1782)

This stuff is more internal, and it's not as important to get done in time for 7.0, but it would still be great to have nice, consistent docs for at some point:

• sopel.coretasks (coretasks: trying to improve docstrings #2001)
  • Proper documentation of everything in here would help core development immensely, even if it's not published in the public API docs
• sopel.loader (loader: improve docstrings #2004)
• sopel.plugins (plugins: improve docstrings according to project standards #2002)
  • sopel.plugins.handlers (plugins: improve docstrings according to project standards #2002)
  • sopel.plugins.exceptions (already done, checked by plugins: improve docstrings according to project standards #2002)
• sopel.test_tools (deprecated, see tests: deprecate test_tools; replace with tests.pytest_plugin #2003)

Note that even though I assigned this issue to myself, anyone should feel free to tackle something on this list in a PR. The review process might be tedious (I'm picky about grammar), but it will all be worth it when we release Sopel 7 and bump the website to show the shiny modern API documentation in all its glory! (Edited to add: We have a preview site which shows the updated docs, but it's not always quite caught up on the latest master changes. We're trying to be nice to our site deployment service by forcing rebuilds somewhat infrequently, since they host us for free.)

[Exirel]

I can't stress enough how much I love this. Let's do this!

[Exirel]

I think in #1697 I worked a bit on that for sopel.irc and sopel.bot.