[Reviewer: Graeme] Craft logging Enhanced Node Troubleshooting 

Added PDLog infrastructure (definition in new header, craft_dcea.h) and PDLogs for http and sip.
The concern was over type-safety.  In the `Log::_write` method, the log text is concise and so can go inline.  This means that even though you have no compile-time type-safety, you can relatively easily check that you have the right number and type of parameters.  In this case, the log is verbose (and has associated cause/effect/action text, so we don't put it inline.  This means that it's hard to police that you have the correct number and type of parameters.  Templating gives this policing.