Merge tag '3.1.1' into develop

Use CGI.escape ratehr than URI.escape to resolve #59
Minor changes to improve support for Ruby 1.9.3 tests
Relaxed gem dependencies; resolves #65
Bump to v.3.1.2
Update CHANGELOG

Added link to #65
Merge pull request #66 from datasift/feature/3.1.2

Feature/3.1.2
Merge branch 'release/3.1.2'