Add C-c C-c as alternative to C-x C-s

[memeplex]

Many modes share the C-c C-c = commit and C-c C-k = abort idiom. I understand the rationale for C-x C-s and it's fine, it already has its complement in C-x C-q. But C-c C-k doesn't have its counterpart in C-c C-c.

So in order to:

1. Be consistent with a large part of emacs that uses the C-c C-c/k idiom.
2. Be internally consistent by providing complete pairs: C-c C-c/k and C-x C-s/q.

I suggest to add C-c C-c.