#121 Full RF64 support

[Michael L]

Dear SoX Developers,

I was recently working on adding full support for RIFF64 files, to work with files bigger than 4 GB.
The changes were mostly made on writeheader in wav.c, it will now add a JUNK chunk if the file is smaller than 4 GB,
if the wav file exceeds 4 GB the RIFF header and data size will be rewritten,
the JUNK chunk will be changed to a ds64 chunk which includes, the riff size, data size, samples written and a table containing other big chunks.

Pros: Full read and write support for RF64 files when reading/writing wav
Cons: All written wav files now 28 bytes bigger because of added JUNK chunk

Best regards,
Michael