0.11's tmux format separator change: post feedback here

[tony]

#343 #298 introduce a new formatting string. libtmux will introduce this in releases after 0.11.0b0 (the first 0.11.0 release)

It is adjustable via LIBTMUX_TMUX_FORMAT_SEPARATOR

You can report any feedback / bugs / improvement ideas here

P.S. This includes finding a portable / compatible default formatter to use. We want something that works across systems and tmux versions