docs: conform docstrings to PEP257

[tseaver]

See: https://peps.python.org/pep-0257/#multi-line-docstrings

Break argument descriptions into separate chunks, and make them more direct.

Also, remove a Python2 compatibility fossil.

[stevepiercy]

The docs build fails on RTD because it lacks a .readthedocs.yaml. See https://readthedocs.org/projects/colander/builds/24402967/

[stevepiercy]

Fixes a few typos and reST and English syntax.

I noticed there is inconsistency between the use of **strong** and *emphasis*. In pylons-sphinx-themes, text with a bold font style is indistinguishable from normal text, due to the chosen font family. I recommend using *emphasis* instead.

From Pyramid docs, this snippet:

https://github.com/Pylons/pyramid/blob/72f61853beda8e21b669c3520e43fe3e5b224ba3/docs/quick_tutorial/requirements.rst?plain=1#L30-L33

* **Workspaces, projects, and packages.** Our home directory will contain a
  *tutorial workspace* with our Python virtual environment and *Python
  projects* (a directory with packaging information and *Python packages* of
  working code.)

Renders as:

https://docs.pylonsproject.org/projects/pyramid/en/latest/quick_tutorial/requirements.html

Note that strong (bold) face renders slightly blurry for normal text, whereas emphasis renders clearly in italic.

Also, now that I've finally figured out how to design Sphinx themes, I created a theme for Plone that could be adapted for Pylons Projects.

• https://github.com/plone/plone-sphinx-theme
• https://plone.github.io/plone-sphinx-theme/