rails4 support and also option to get more conditional hashtaggable Value

Following are the changes:
- Rails4 support with protected_attributes
- add the optional parameter to the hashtaggables method so that users can pass the conditions they want on the hashtaggings table.
- Older version compatibility, it will work, because I made the argument optional with accept hash.
- Test coverage for the above functionality.

Let me know if you find any issue in the code.