Prepare release notes for Libav 10 "Eks"

Additional editing by Diego Biurrun
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  Prepare release notes for Libav 10 "Eks"

Conflicts:
	doc/RELEASE_NOTES

Not merged because all that stuff has been in past releases

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/pngdec: fix signed overflow

fixes fate ftrapv failure

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>