emacs: cleanup and customization

- Add ace-jump-buffer(key -> C-x SPC)
- Add smart-operator
- Remove unwanted paredit config
- other cleanup

Signed-off-by: Ratheesh S <ratheeshreddy@gmail.com>
emacs: add smex to emacs

Add smex to emacs

Signed-off-by: Ratheesh S <ratheeshreddy@gmail.com>