This contains various RST reformatting.

One, moving `(C)` one line up, is specific to a bug in tree-sitter-rst
that mis parses this section. Another is adding one black line for a
similar reason where `..` is seen as section underline by
tree-sitter-rst.

This is some shuffling of section underline: try to be consitant,
`=`, then `-`, then `~`, with this refactor there is also no more
section that use backticks as underline.

Note in particular that non-consitency of underline lead to a problem in
datetime64 section where "weekmasks" (underlined with `-`) were actually
a level-4 heading instead of a level 2 or 3 I guess, and thus were
nested under the `busday_count()` section.

You'll note also 2 formulas that are under double-quotes as they are not
references.