[Grml-devel] Add tmux config to grml-etc-core

[Sebastian Boehm]

Here's a tmux.conf for inclusion in grml-etc-core.

Since everybody in #grml seemed to agree that it was a good idea to
set the prefix keybinding to C-a (instead of the default C-b), I went
ahead and did just that. The other settings should be less
controversial.

It would be great to have a good tmux config in grml-etc-core and
while there's certainly room for improvement, I feel that this patch
should be a good starting point.

Regards
Sebastian