All parameters for #create in PostsController pass through strong_parameters.

We are now explicitly whitelisting all parameters for Post creation. A nice side-effect is that it cleans up the #create action in PostsController. We can now trust that all parameters entering PostCreator are of a safe scalar type.
Merge pull request #979 from iancmyers/strong-parameters

All parameters for #create in PostsController pass through strong_parameters