More refactoring / documentation

- Bumped version to 1.1.1
- Refactored "taggable" method into cleaner sub methods
- Added method documentation
- Merged "GroupBy" code into main class
- Added CodeClimate badge
- CodeClimate GPA now at 4.0

As part of the GroupBy merge, this syntax now throws and error:
   ```ruby
   class Invalid
      include Mongoid::Document
      include Mongoid::TaggableWithContext::GroupBy::TaggableWithContext  #ERROR!
   end
   ```
   ```ruby
   class Invalid
      include Mongoid::Document
      include Mongoid::TaggableWithContext::GroupBy::AggregationStrategy::RealTime  #ERROR!
   end
   ```

Instead you need to do this:
   ```ruby
   class Valid
      include Mongoid::Document
      include Mongoid::TaggableWithContext
      include Mongoid::TaggableWithContext::AggregationStrategy::RealTimeGroupBy
   end
   ```