Misc fixes I had in my local copy
HIDE_WINDOW setting

When enabled, it will create the window at index 9999 and remove
formatting/title to make it invisible.

If something breaks and tmux-url-select doesn't start, you can always
switch back to that window, with, say, tmux choose-window, or anything.
Add o, O and Y commands

o: open link, alias for enter
O: open link, don't close
Y: yank link, don't close

Also fix behavior when yank would switch back without exiting.