This keeps tripping people up. We can't mention it *everywhere*, but
lets see if it works just in "match", since that sees to be where
people hit it most.
This allows linking them from elsewhere (currently fish_indent) and
also improves the formatting - the code formatting here isn't actually a good look.
This now means `abbr --add` has two modes:
```fish
abbr --add name --function foo --regex regex
```
```fish
abbr --add name --regex regex replacement
```
This is because `--function` was seen to be confusing as a boolean flag.
This committed the sin of introducing a concept by giving it two
names:
> An alias, or wrapper, around ``ls`` might look like this
The term "wrapper" doesn't pull its weight here. It's simpler to just
call them aliases throughout. We do use "a simple wrapping function"
in another place, but that's to define "alias", not as a separate name.
Also default the marker to '%'. So you may write:
abbr -a L --position anywhere --set-cursor "% | less"
or set an explicit marker:
abbr -a L --position anywhere --set-cursor=! "! | less"
This renames abbreviation triggers from `--trigger-on entry` and
`--trigger-on exec` to `--on-space` and `--on-enter`. These names are less
precise, as abbreviations trigger on any character that terminates a word
or any key binding that triggers exec, but they're also more human friendly
and that's a better tradeoff.
Prior to this change, abbreviations were stored as fish variables, often
universal. However we intend to add additional features to abbreviations
which would be very awkward to shoe-horn into variables.
Re-implement abbreviations using a builtin, managing them internally.
Existing abbreviations stored in universal variables are still imported,
for compatibility. However new abbreviations will need to be added to a
function. A follow-up commit will add it.
Now that abbr is a built-in, remove the abbr function; but leave the
abbr.fish file so that stale files from past installs do not override
the abbr builtin.
