Rewrite the `abbr` function to store each abbreviation in a separate
variable. This greatly improves the efficiency. For the common case
it is 5x faster. For pathological cases it is upwards of 100x faster.
Most people should be able to unconditionally define abbreviations in
their config.fish without a noticable slow down.
Fixes#4048
The abbr function doesn't have the possiblity to rename abbreviations.
You have to delete the old one and create a new one. This commit adds
this functionality and uses the syntax:
abbr -r OLD_KEY NEW_KEY
Fixes#2155.
People regularly ask how to make abbreviations global (i.e., private to
a fish session) rather than universal. So explain how to do so in the
`abbr` man page.
Fixes#3446
We silently upgrade existing abbreviations and change the separator when
saving.
This does not yet warn when the user is using the old syntax.
Resolves#2051
Support for space-delimited abbreviations was added to the expansion
parser in fbade198; this commit extends that support to the user-facing
tools, and documents the space-separated behaviour. Equals-delimited
abbreviations are expected to be removed before the next release.
Work on #731.
