- added u_fillable on models used in tests that need it
- added documentation for mass assignment
- added tests for mass assignment feature
- added new Torrent models for tests, which have set up u_fillable and
u_guarded differently
- added schema grammar, query post-processor, and schema builder, they
was needed for database column listing during a mass assignment
guarded attributes check, used to check if the given attribute is
a valid guardable column
silverqx