r embodiments, the invention provides a compound according to <1> or salt thereof, wherein Ar is a group represented by the formula: [wherein R11 and R15 have the same definitions given above, and R16 represents (1) hydrogen or (2) a group selected from Substituent Group H above, and R11 and R15 or R15 and R16 may bond together to form a 5- to 6-membered heterocycle optionally substituted with at