DWAA/DWAB Compressions

[Jovp]

Would be great to create the DWAA and DWAB compression constants to be used when writing files

For now one needs to do:
pyexr.write(path,data,precision,compression=Imath.Compression(Imath.Compression.DWAB_COMPRESSION),extra_headers={"dwaCompressionLevel":50.0})
to be able to use these.
Also note the compression level header, maybe this could be made an argument.