Support newer versions of Hashie

This builds on #11, and fixes #10 more completely.  Herein we change the Hashie version requirement to ">=3.3.1" (latest tagged version) and "< 3.4.0".

I used rvm to manually test against Ruby 1.9.3, 2.0.0, and 2.1.3.  The overtest task didn't work on my system.

These commits bump the gem version to 1.2.0 due to the change in Hashie version to avoid collisions in code dependent on this gem.

If you merge this pull request directly, #11 can be discarded, or you can merge #11 first and then this one.