Parsing ad hoc regex in query string

[vovcacik]

Extracts strings from fzf items using a regex template written directly in query /stash..../. In fzf's syntax the template would probably look more like {/stash..../}.

In the example, the regex template is used instead of positional parameter, because positional parameter includes the trailing colon. Git will error on git stash show stash@{0}:. Browsing the git stash is just for context; also the example could be solved with --delim ":" {1}, but that's not my point.