Behaving more like ActiveRecord.

- We fail loudly when save! is used.
- We don't save when validations fail
- We can skip validations passing in {:validate => true}

hi!  This is in reference to: https://github.com/sxross/MotionModel/pull/17 

I needed to add that def save(*) in order to be able to pass in the Hash to skip the validations like ActiveRecord. I hope it is ok.  :+1: