Attributes should respect symbolize_key config

@soulcutter would love to get your thoughts on these changes which should close issue #20, I also added a few other specs I did not see.  The version has been bumped to `0.9.5`.
Understandable - I almost always make version bumps their own commits that correspond with the approximate time of rubygems releases / version tags. Also branches sometimes get merged out-of-order, so if versions are included it gets weird if you aren't mindful. Thanks for your thoughtfulness, though!