Updated copyright notices

libcelt/arch.h

libcelt/bands.c

libcelt/bands.h

libcelt/celt.c

libcelt/celt.h

libcelt/celt_header.h

libcelt/cwrs.c

libcelt/cwrs.h

libcelt/dump_modes.c

libcelt/ecintrin.h

libcelt/entcode.c

libcelt/entcode.h

libcelt/entdec.c

libcelt/entdec.h

libcelt/entenc.c

libcelt/entenc.h

libcelt/fixed_debug.h

libcelt/fixed_generic.h

libcelt/header.c

libcelt/kfft_double.h