Show CPU load average and memory usage in the status bar. CPU load average comes
straight from uptime (essentially the same load average information you see in
top). The memory statistic roughly represents the amount of RAM that is
currently in use and cannot be recovered, and is calcuated from /proc/meminfo
via MemTotal - (MemFree + Buffers + Cached).
The refresh rate defaults to 5 seconds, but this can be modified by changing
REFRESH_PERIOD in extension.js.
Initial release.