Added cjdns

cjdns - Caleb James DeLisle's Network Suite
https://github.com/cjdelisle/cjdns
http://cjdns.info

A tool for building physical or virtual meshnets through the use of
IPv6 tunnel interfaces on Unix systems.

 - Fixed the previous issue with `superenv`, the formula now includes `env :std`.
 - Fixed style issues (whitespace, parenthesis, etc.)
 - Added the head URL back into formula