add support for 64bit WAVE files

[Rengati]

[Rengati]

Hi, Thanks for this librairy, I have added a support for 64bit WAVE files for my personnal use and I think I could be useful to other people. If the pull request is not in the correct format please let me know and I will make the necessary changes.

[adamstark]

Hi there, thanks for this pull request. It looks good - am I right in thinking that IEEEFloat can refer to either 32-bit or 64-bit encoding? Or is there a separate encoding flag for 64-bit floats?

I will also need to write some unit tests for this too, but I'll try and do that soon :)

[Rengati]

Hi, Yes you are rigth, IEEEfloat works the same way for 32-bit and 64-bit (cf. https://en.wikipedia.org/wiki/IEEE_754#Basic_and_interchange_formats)