Adds synopses for those commands missing them.
Moves all synopsis sections to code blocks. This improves the appearance, although highlighting as
fish code may not be the ideal appearance.
Allows `fish_indent -w **.fish` to restyle all fish files under the
current directory.
(This also has the sideeffect of reducing style.fish time by ~10s, as
we only need to invoke `fish_indent` once, instead of once per-file)
