Use read-kbd-macro instead of kbd as a function.

In Emacs 24.1 and 24.2, kbd was a macro and not a function,
so that a call like (kbd (format ...)) would fail. Use
read-kbd-macro instead, which works for all Emacsen in 24.x.
Merge pull request #191 from jorgenschaefer/master

Use read-kbd-macro instead of kbd as a function.