add license information to gemspec

This way you can find this information with the rubygems.org API
Merge pull request #58 from jordimassaguerpla/master

add license information to the gemspec
bump to latest headers, close #63
update travis image
tests
allow set history filename
thanks :)
make contributing policies more known
Bump to version 1.3.2
Bump to version 1.3.3