Add serialization_options

Prior to 0.9, @options was used to see the options passed to to_json. For some reason, with 0.9 the options were no longer passed and were entirely inaccessible within a Serializer.

This restores the access by placing it in an attribute named serializer_options.
Fix serialization_options for array serialization
Make options param optional
Make sure serialization_options is never nil
Test to cover serialization_options
Merge pull request #679 from Ahalogy/serializer-options

Serializer options