Represents a CouchDb document
initializes a new document object with attributes as the document values
Look up an attribute by key
Set an attributes by key to value
yields each document attribute
is the attribute key in this document?
Sets the id to new_id (Only for internal use really, but public nevertheless)
is this a new document?
Saves this document to the database
Converts the Document to a JSON representation of its attributes
[Validate]