add license information to the gemspec
add license information to the gemspec

This way it can be queried using the rubygems.org API

107191613/addressable,davidbegin/addressable,rkh/addressable,sporkmonger/addressable,sferik/addressable,shaicoleman/addressable,EiNSTeiN-/addressable,Hacker0x01/addressable,iainbeeston/addressable