* BREAKING CHANGE: Default value for `updated_accessor` was `:updator`, is now `:updater`, since "updator" is not an English word
* Replace usages of `id` with `_id`, since there are many gems which override the behavior of `id`, for example "mongoid_slug"
* Rename `Mongoid::Userstamp.configuration` and `Mongoid::Userstamp.configure` to `#config` which is both a getter and a setter. `#configure` is now an alias `#config`
* Do not overwrite creator if it has already been set manually
* Define setter methods for updated_accessor/created_accessor which assign the underlying field to the user id. Accepts both Mongoid::Document and BSON::ObjectID.
* Support optional Mongoid field alias for updated_column/created_column, which is useful when working with minified column names
* Expose current_user as Mongoid::Userstamp.current_user
* Field type is now ::Moped::BSON::ObjectID instead of Object
* Improve code readability
* Improve test coverage, including adding tests for configuration