taggregator 0.1.0

Taggable in context and aggregation of tags for MongoMapper. Adds weight and distribution convenience methods to models in which it is included. Uses MongoDB's increment/decrement ($inc/$dec) to keep real-time counts of individual tags in context with optional type. Based on 'Mongoid Taggable With Context' (https://github.com/aq1018/mongoid_taggable_with_context).