It's purpose is to show entered keystrokes during entering key-combos.
It's positioned at the bottom-right corner (similarly as in vim). Many
thanks to @bram85 for the idea.

Also fixed one nasty bug resulting in getting stuck in keystate. It
occured only when keystate had also corresponding pending action and
user typed something other than expected by the keypress(). Now any
non-sensical input will result in resetting keystate.