def copy(dest)
      raise ArgumentError, "doc.database required to copy" unless database
      result = database.copy_doc(self, dest)
      result['ok']
    end
def copy(dest)
      raise ArgumentError, "doc.database required to copy" unless database
      result = database.copy_doc(self, dest)
      result['ok']
    end
copies the document to a new id. If the destination id currently exists, a rev must be provided.
 <tt>dest</tt> can take one of two forms if overwriting: "id_to_overwrite?rev=revision" or the actual doc
 hash with a '_rev' key