We are adding quantization with the bitgroom filter to the netCDF C/Fortran libraries (see Unidata/netcdf-c#1548)

I have a PR up for the C library (Unidata/netcdf-c#2088) and one for the Fortran library (Unidata/netcdf-fortran#304) and each of those have documentation changes supporting the new quantize functions.

I would also like to add a section to the language neutral docs, but I'm not sure where in this repo I should do that. It should be near wherever compression is explained.