Shorten context to ctx

Shorten context to ctx

(This breaks the API.)

"context" is really annoying to type all the time (and we're going to
type it a lot more :). "ctx" is clear, concise and common in many other
libraries. Use it!

Signed-off-by: Ran Benita <ran234@gmail.com>
[daniels: Fix for xkb -> keymap change.]