Adds some communication and networking libraries

I've added some Contributed Libraries from the communication and networking section of the Arduino Libraries page http://arduino.cc/en/Reference/Libraries.

After doing this I have a suggestion and a question. :)

Suggestion. Please consider adding a "tutorial" field to the JSON document used for the libraries. Some of the library home pages do not have tutorials, such as the SerialControl library's GitHub page. In that case it would be nice to be able to add a URL pointing to the Arduino site's SerialControl tutorial at http://playground.arduino.cc/Code/SerialControl.

Question. Does the "location" field always have to refer to a direct file download or a Git repo? For example, I want to add the xbee-arduino library at https://code.google.com/p/xbee-arduino/ but the downloads are provided via Google Drive and I found it impossible to get a "direct" URL for the library's downloads.

Thanks!