tmux-continuum run at startup on linux

[ghost]

Started with adding tmux-continuum run at startup support for linux OSes. Given the diversity of linuxes, a larger effort will be required in getting a fully supported implementation working. As such, I've laid the basic groundwork that is effectively the same on all linuxes, (nixes for that matter) and what remains is implementing a cross platform startup scripting method. As an Ubuntu and CentOS user, I can do this for my OSes but I can't be certain that it will work across the board, and I'm certain it won't for any Slackware based distros.

[jpickwell]

On Ubuntu Server 14.04, I have the following at the end of my .bashrc file:

# run tmux, but only if we're not inside tmux (prevent endless loop)
if [ -z $TMUX ]; then
  TMUX= tmux -2 new
fi

My feeling is that if you're using a GUI, then you really only need tmux to start when the terminal starts.