Switch to using uvmexp which is the prefered way of retrieving memory information
Switch to using uvmexp which is the prefered way of retrieving memory information

Also fixup some page shifting and casting issues which led to incorrect
amounts of memory being displayed. This also fixes a crash with --colors (#20)

allcatsarebeautiful/tmux-mem-cpu-load,allcatsarebeautiful/tmux-mem-cpu-load,allcatsarebeautiful/tmux-mem-cpu-load,thewtex/tmux-mem-cpu-load,thewtex/tmux-mem-cpu-load,thewtex/tmux-mem-cpu-load,allcatsarebeautiful/tmux-mem-cpu-load,thewtex/tmux-mem-cpu-load