Prepared gem structure
Modeled initial specs of Entity, EntityDescriptor and Attribute
Mixed some metaprogramming to easily add more data types to EntityDescriptor
Added some options (with defaults) to the attribute object structure
Enabled the whole set of data types allowed in CoreData to be defined for each new attribute
Attribute's properties are now read-only
Added the name property to the EntityDescriptor class
Adjusted the EntityDescriptor's name assigning to convert symbols to strings
Defined the 'create_entity' method for the Entity class (?)
Renamed the Entity class to 'EntityDefinition'
Additional specs for EntityDefinition#create_entity
EntityDescriptor#xml_attributes used to return an entity node's attributes
Attribute#xml_attributes specs implemented
XML building of EntityDescriptors and Attributes