#36: Add 'Active Under Contract' to ListingStatusEnum and update documentation to align with Data Dictionary; Add MlsStatus from Data Dictionary

On 2013-08-14, the Syndication WG voted to add a patch submitted by James Martin to better align the Syndication schema with the Data Dictionary. The patch has a new enumeration value for off-market, accepting offers and a field MlsStatus which holds the MLS specific status name.