Make keymap an optional argument of modalka-define-key

[KaiHa]

With an optional keymap argument it is possible to also create prefix
commands in "normal" mode. Eg. like a mapping from x s to C-x C-s:

(let* ((keymap (define-prefix-command 'modalka-Control-X-prefix)))
  (define-key modalka-mode-map (kbd "x") keymap)
  (modalka-define-key (kbd "s") (kbd "C-x C-s") keymap))

Note, that I am by no means an Emacs wizard, so it is quite possible
that this can be achieved much simpler or cleaner or is a total stupid
idea altogether.

Related to #25.

[mrkkrp]

But that's already supported:

(modalka-define-kbd "x s" "C-x C-s")

[KaiHa]

But that's already supported:

(modalka-define-kbd "x s" "C-x C-s")

Ohh, then disregard my request. I simply didn't know that this was already possible. Nice work

[mrkkrp]

No problem!