Add option to terminate on specific character in search

[lewisthompson]

Assuming the following directory structure:

% tree .
.
├── b
│   ├── c
│   │   └── g
│   │       └── h
│   │           ├── j
│   │           └── k
│   └── d
└── e
    └── f

9 directories, 0 files

When in dir b/c/g/h/j with FZF_COMPLETION_TRIGGER='':

/tmp/b/c/g/h/j % cd ../<PRESSED_TAB>
> 
  2/2
> ../j
  ../k

Above I am using tab completion to get a listing of available directories to cd into. I quickly realise that I wanted to go a directory (or maybe more) further up the stack. My instinct is to type ../<TAB> as I would with standard bash/zsh tab completion. However, with FZF these keystrokes get passed into the search filter and I must instead press ^C and the ../<TAB>. Having to press ^C repeatedly gets old quickly.

My feature request is the ability to specify a character via the commandline that would immediately terminate fzf with a zero exit code. For this example let's name the argument --exit0-char.

In my .zshrc I would set export FZF_COMPLETION_OPTS='--select-1 --exit-0 --exit0-char=." which would be automatically picked up by __fzf_generic_path_completion in completion.zsh and offer (IMO) greatly enhanced path completion.

[lewisthompson]

--bind='.:abort'" is extremely close to what I want here. The major downside is that the . entered to abort fzf does not get appended to the path. I tried mucking around in __fzf_generic_path_completion but couldn't come up with anything entirely satisfactory.