This commit expands quick select mode so that you can trigger it
with distinct sets of patterns (eg: urls on one key assignment,
hashes on a different key assignment), different alphabets,
and lastly, the option to perform a different action from
the default copy action.
You can pair this with `action_callback` to run lua code to
do something with the selected text.
This commit also adds `wezterm.open_with`, a helper function
for opening documents/URLs.
refs: #846
refs: #1362
* Make alphabet and patterns configurable
* add docs
* Enhance scrollback search to support regex captures so that
searching for eg: `fo(o)` will select the last `o` in `foo`.
refs: https://github.com/wez/wezterm/issues/732