per the sass-lang docs [1], the user should be able to invoke
`map.get($my-map, "key1", "key2")` to perform a nested lookup
of the two keys. the current implementation fails if provided
more than two arguments to `map.get`. this change implements
the nested get. fixes#80.
[1] https://sass-lang.com/documentation/modules/map/
this change does fix more number tests, but i'm not certain that
it doesn't break cases we don't test for.
it only solves extremely niche edge cases, so for now reverting
until we can be more certain in a later release
