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.
* Prevent not-yet-loaded functions from loaded when erased
Today, `functions --erase $function` does nothing if the function
hasn't been autoloaded yet.
E.g. run, in an interactive session
> functions --erase ls
> type ls
and be amazed that it still shows our default `ls --color=auto`
wrapper function.
This seems counter-intuitive - removing a function ought to remove it,
whether it had been executed before or not.
* doc/changelog
