Add support for Mac OSX from Justastic. Refactors the code from Justastic so it
works with the Linux code and so it also works for the new colors support.
Still need to test on OSX.
Conflicts:
tmux-mem-cpu-load.cpp
Colors are added for terminals that have 256 color support when the
--colors flag is enabled. The background colors are varied with different color
maps derived from their matplotlib versions. The foreground color is a
contrasting black or white.
