Changelog: add nuts side & metadata support

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/mathematics: add av_add_stable()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avutil/rational: av_add_stable() test code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/utils: fix rounding error accumulation for generated dts in compute_pkt_fields()

This only updates the case where there is no B frame reordering delay.

Tested-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>