I can't shutdown anything, except my own Linux box. The source is almost ready to be portable, I just lack information to do it. Currently, the main problem is the centralized static variable-set. I don't know if I'll ever do it, I suppose it depends on the amount of feedback I get. Browse the sample configuration file.
Some skeletal information is in the manual page, but the sample file is still the reliable doc.
Ideally, your bootstrap files should invoke powerd with no arguments, while the commandline is meant to be used for testing purposes. The configuration file is not read. This is independent of the agent used, which is specified by the previous options or by the configuration file. Any agument embedding an equal sign is used like it was a line of the configuration file. Note that powerd and powerd.conf must reside in the root filesystem in order fro your computer to be able to wake up from singleuser-ness.