opusdec decoding to wav files over 3 hours results in truncated audio, support for rf64

[eharris]

opusdec seems to write wav files that exceed the limits of wav/RIFF without any notification or warning. The resulting files appear to contain all the audio data, but anything that reads the resulting files just gets truncated audio because the RIFF header only supports the limits of the original RIFF format.

When writing wav files larger than the limits of the RIFF format, opusdec should write them with an RF64 header, which supports file sizes over 4GB and is an accepted ITU standard.