Specialized hash implementation

[sbellware]

Schema objects can't be used with Set implementations (whether Ruby's or Eventide's) because of a lack of a specialized implementation of the hash method needed to generate a consistent hash key.

Calculate the hash value by first creating a representation of the raw attributes, and then deriving a hash key from that data.

Consider adding a raw_attributes method to the Schema module, and/or augmenting the existing attributes method with a boolean transform (defaults to true) parameter to control whether the attributes are subject to any transformation logic.