More cpu system checks / documentation

[dAniel hAhler]

Hello,

currently there are "cpu usage" tests for "user", "system" and "wait".
They are not really documented on
http://www.tildeslash.com/monit/doc/manual.php, there's just an
example.
But looking at the source code shows that only the above three
variants seem to be available.

What I'd like to use would be e.g. "cpu usage (idle) < 5% for 10
cycles" or something similar.

Does this make sense? It seems like it would be quite easy to add.

Thank you.