Revert "revise for mac"

This reverts commit f6f7ec51639290ad28f2568ad1225721c58e1ae0.

$ brew install xz
$ brew install coreutils
cosmetic change

 * $ARCH -> $PLATFORM
 * add osx and unknown
enable to work on osx
add submodule tmux-mem-cpu-load
enable to work on osx
add the tmux-mem-cpu-load to the status line