PYTHON-346 - Use a tuple for decoder options.
PYTHON-346 - Use a tuple for decoder options.

This is just a cleanup of the existing decoder. I tried
using a namedtuple but that imposed up to a 17% perf hit
(a regular tuple imposed no measureable perf hit). We may
be able to avoid that problem with a new API that accepts
decoder options in a specific class instead of creating the
instance in the decoder itself.

jameslittle/mongo-python-driver,ShaneHarvey/mongo-python-driver,brianwrf/mongo-python-driver,inspectlabs/mongo-python-driver,macdiesel/mongo-python-driver,develf/mongo-python-driver,bq-xiao/mongo-python-driver,ameily/mongo-python-driver,ShaneHarvey/mongo-python-driver,mongodb/mongo-python-driver,gormanb/mongo-python-driver,aherlihy/mongo-python-driver,pigate/mongo-python-driver,ShaneHarvey/mongo-python-driver,develf/mongo-python-driver,ramnes/mongo-python-driver,mongodb/mongo-python-driver,WingGao/mongo-python-driver,felixonmars/mongo-python-driver,gormanb/mongo-python-driver,aherlihy/mongo-python-driver,ultrabug/mongo-python-driver,inspectlabs/mongo-python-driver,pigate/mongo-python-driver,felixonmars/mongo-python-driver,ramnes/mongo-python-driver,WingGao/mongo-python-driver,bq-xiao/mongo-python-driver,ramnes/mongo-python-driver,llvtt/mongo-python-driver,jameslittle/mongo-python-driver,rychipman/mongo-python-driver,aherlihy/mongo-python-driver,brianwrf/mongo-python-driver,ameily/mongo-python-driver,rychipman/mongo-python-driver,macdiesel/mongo-python-driver,llvtt/mongo-python-driver,ultrabug/mongo-python-driver,mongodb/mongo-python-driver