Keyboard layout switcher for StumpWM

** Usage
Add 
#+begin_src lisp
(load-module "kbd-layouts")
#+end_src
to =.stumpwmrc= 

You can specify your keyboard layouts using the function
=KEYBOARD-LAYOUT-LIST=. Layouts are represented by strings identical to
those used by setxkbmap, e.g.:
#+begin_src lisp
(keyboard-layout-list "us" "pl" "ru -variant phonetic")
#+end_src
This will also immediately select first layout from the list.

You can also specify the behavior of the CapsLock key using
variable =*CAPS-LOCK-BEHAVIOR*=. Available are the following values:
- =:normal= - CapsLock serves as CapsLock
- =:ctrl= - CapsLock serves as additional Ctrl
- =:swapped= - CapsLock and Ctrl are swapped
- =:leave-alone= - do not change CapsLock with setxkbmap
Add for example:
#+begin_src lisp
(setf kbd-layouts:*caps-lock-behavior* :leave-alone)
#+end_src
Note: If you do change =*CAPS-LOCK-BEHAVIOR*= add the call before
the call to =KEYBOARD-LAYOUT-LIST= in your config file, to have it
affect the initial configuration of your keyboard.

By default the command =SWITCH-KEYBOARD-LAYOUT= is bound to the key
combination =s-SPC= (=WinKey-Space=).
