tmux.conf now works correctly for linux

Moving out the macosx specific part to tmux-osx.conf
remove the ruby prompt segmenet on the far right.
tmux configuration improvements.

Improve how the file is organized - it was a mess before!
Gist configuration so that it's more useful as a browser.
Makes Shift + Enter work. With Magus iTerm2 Configuration.

The way this works is that the actual keybinding is a weird character,
and on our iTerm configuration we map <S-CR> to submit it.

Effectively allowing us to use Shift on the Terminal.
Remove terminal from prezto - it was doing unexepcted things.
iTerm2 Configuration Updates.