Patch: Add `evil-toggle-key'

Hi List, I don't switch between evil states and emacs states quite often and so use C-z for a more used command.[1] In viper there was `viper-toggle-key', appended is a patch to add `evil-toggle-key' and adjust the keys to it. Michael Footnotes: [1] Yes I can redefine them myself, but that results in 4 quite ugly lines.