Reformat unordered lists in all docstrings

WIP for #2411. Pushing this to get initial feedback.

I did a visual check of the rendered docs (generated by stock html formatter and my pandoc+sphinx combo) for some pathological modules (File, GenServer, Module, Regex). They seem to be consistent.

/cc @ericmj @jwarwick

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List items are marked with a star (*). Bullets marking list elements
must have a 2-space indent. The continuation lines should be indented
by 2 more spaces.

The second and subsequent paragraphs need to be indented 4 spaces
from the beginning of the line to be included in the list item.

The code fragments have to be indented 8 spaces from the beginning
of the line (or 4 spaces from the beginning of the preceding paragraph).

Sublists are marked with a hyphen (-). They follow the rules above
with the difference that their initial indent will be greater
(8 spaces from the beginning of the line).