[libxkbcommon] Pull request - many changes

[wettstein509 at solnet.ch]

> At the moment it just means they won't work in Wayland, but support
> might (might) be removed from the X server at some stage too.  Is
> there any reason you can't just use a locked group or level rather
> than an overlay?

I currently use overlays to have five layouts in my keymap, which is not
possible with using groups alone.  Admittedly, this is more for fun than
really useful, but I have seen that some people require more than the
four groups that XKB supports.  Overlays allow to work around this
restriction.

Another use of overlays you will see when you try to put control keysyms
or keypad keysyms (such as Next and KP_Add) on a higher level of a
"usual" key (see, for example, de(neo) in xkeyboard-config).  This
creates trouble with various applications (for example, Xt applications
such as xterm).  If one uses overlays instead of levels, these problems
can be worked around.  Redirect actions are an even more powerful
alternative, but they are harder to use.

Andreas