Added colors to tmux.

I decided to finally take the plunge and change the colors of tmux. I
figure since I look at tmux so often, it's a good idea to have it look
pretty. I started off by copying [tmux solarized][1] for inspiration.
However, I wasn't super fond of the choices. So, I looked up the
different colors tmux had available with help from [this stack overflow
question][2] and chose a set of colors that I liked. I went largely with
red to match xmonad's colors.

[1] https://github.com/seebi/tmux-colors-solarized/blob/master/tmuxcolors-256.conf
[2] http://superuser.com/q/285381