A first pass at adding some ahcp options

This:

Adds -h for help
Extends the -P option (request prefix delegation) to take arguments
(kind of unclear if /24 is disambguiated from ::/24 at the moment)
Adds some support for prefixes throughout the stack
(the use of the configuration struct inside the packet struct
 inside of message processing I find rather confusing)
re-organizes the parser a bit

Adds a message for a name request