Update copyright in libdecnumber.

libdecnumber/ChangeLog

libdecnumber/Makefile.in

libdecnumber/bid/bid-dpd.h

libdecnumber/bid/bid2dpd_dpd2bid.c

libdecnumber/bid/bid2dpd_dpd2bid.h

libdecnumber/bid/decimal128.c

libdecnumber/bid/decimal32.c

libdecnumber/bid/decimal64.c

libdecnumber/bid/host-ieee128.c

libdecnumber/bid/host-ieee32.c

libdecnumber/bid/host-ieee64.c

libdecnumber/configure.ac

libdecnumber/dconfig.h

libdecnumber/decBasic.c

libdecnumber/decCommon.c

libdecnumber/decContext.c

libdecnumber/decContext.h

libdecnumber/decDPD.h

libdecnumber/decDouble.c

libdecnumber/decDouble.h