Prepare for 0.4.3 release
Fixed #47: use a database index when generating proxy binding in Garner::Mixins::Mongoid::Identity with multiple Garner.config.mongoid_identity_fields.
Merge pull request #49 from dblock/issue-47-limit-one

Fixed #47: use a database index when generating proxy binding in Garner::Mixins::Mongoid::Identity with multiple Garner.config.mongoid_identity_fields.
Preparing for a 0.4.4 release.
Changed numbers in the README to say 0.3.x and 0.4.x to avoid having to change this every time.