Model before_update callback was not defined.
Index hash_key values were empty because of the key used.
Hash keys are converted to_sym.
Update persistent to use update callbacks.
Update .gitigore for RubyMine.
Merge remote-tracking branch 'origin/master' into before_update_fix

Conflicts:
	lib/dynamoid/persistence.rb
Merge pull request #123 from stefanneculai/before_update_fix

Model update callbacks were not defined.
Merge pull request #124 from stefanneculai/fix_index_hash_key

Symbolize keys passed to Chain#where()
Update attributes can get an empty array
Merge pull request #136 from stefanneculai/fix_update

Update attributes can get an empty array.
subclassing support
set type field automatically
need to check class, not instance, for attributes. durp!
Support for removing fields after they've been defined
Add support for STI sub-classes to have additional fields