check and update web links

Given a new release happening, it would be nice to check and update some links, here are some examples:

• 130 occourences http://www.xiph.org -> https://www.xiph.org (https). Note: some are in the IETF RFCs, probably should not be changed, given they should match what was published
• 1 occourence http://xiph.org/ogg/ -> https://www.xiph.org/ogg/ (https + add www. for consistency with the others)
• 11 occourences http://www.theora.org -> https://www.theora.org
• 11 http://www.ietf.org -> https://www.ietf.org
• 46 others to individually check and review