Modified cpu_mem_usage optionally output used (non-free) memory.

Added a -u/--used/--used-mem flag to optionally show the used
(non-free/active & inactive) memory, instead of just the active memory.
Add track_timeout, notification of screensave active period.

Small script that used 'xscreensaver-command -watch' to notify the user
how long xscreensaver has left the screen blank for - work out how long
you've been distracted!