doc: update blog post URL

dump: add a timestamp to help compute CPU usage

The timestamp is from an unspecified fixed start point. It is the result of a
monotonic clock. On Linux, this is from boot time.

top: safety measure to avoid infinite loop

dump: don't call cg_cpu_usage() twice

dump: add "dump" command to dump all info in JSON

top: add a top command

No sorting, but CPU usage with a nice bargraph.
Requires curses.