Fixes #51 (ctrl-c bug)

Adds ctrl-c to the list of characters that exit streak mode without a
fall through to vim. That fall through is most likely the cause of the weird state you encountered in #51. Not worth thinking about that problem, ctrl-c causes all kinds of havoc when plugins, autocmds etc are used.

Anyway, all is fine when ctrl-c is added to this list, I assume that's what you intended to do anyway :)