The Plug and Play release

Add a brand new app: gspnp_responder found in plugnplay. Supports the Grandstream Plug and Play protocol in either passive mode (just reports phones as they boot) or will optionally send back a profile URL so the phone can configure itself. See the README in the plugnplay folder.

Improve the documentation, but still a ways to go with the Phonebook and pvalues-to-XML converters.