Implement #'exwm-buffer-groups-kill-buffer
Invoke '--remove-buffers before listing buffers
"nil" has been showing up recently when I hit <C-x b>, presumably
because 'buffer-name for a dead buffer returns 'nil. No big deal, we'll
just call exwm-buffer-groups--remove-buffers before giving a list of
buffers in the completing read. This *might* not be the most elegant
solution, in which case I'll hopefully come up with something better
later on.
Fix exwm-buffer-groups-move
The original version of the function didn't actually modify
'exwm-buffer-groups-buffers.
Implement exwm-buffer-groups-switch-buffer
Implement exwm-buffer-groups-move
Use 'cl-lib instead of the deprecated 'cl