Catch up on upstream's round/roundf/roundl.

Not sure how we missed these, but better late than never...

Change-Id: Ib08d1bb6e340a1907cbeb1cbe220e33f70642bdc
Merge "Catch up on upstream's round/roundf/roundl."
Improve documentation for testing and coverage.

Also rename HACKING.txt to README.md so it will display on the GitHub
mirror.

Change-Id: I70157a4ad262700212bf9afd87253d195c7013a9
Merge "Improve documentation for testing and coverage."