Thread safe support
Merge pull request #463 from billychan/replace-class-variables

Thread safe support
Add option to order by number of matching tags.

- Adds :order_by_matching_tag_count to tagged_with method
Merge pull request #469 from ExamTime/master

Featured added: Option to order by number of matching tags.
Let '.count' work when tagged_with is accompanied by a group clause
Merge pull request #417 from okgrow/fix-group-by

Fix: Let '.count' work when tagged_with is accompanied by a group clause
Updated CHANGELOG.