Fix Deser for Other Attributes

[Benjscho]

Deser failed for other attributes because they were missing the untagged marker.

Fixes #52

[Benjscho]

Actually on testing looks like this is representing the other attribute types as Other too:

                Other(
                    "#[non_exhaustive]",
                ),

need to fix that.

[Benjscho]

I had a crack at a manual deserializer, but I absolutely might missing something about the crate and the implementation.

In general I'm looking for a way to access which features are needed for an item. Let me know if there's a way I could help with implementing that! I'm guessing there might be some work to reimplement or copy how rustdoc handles cfg_attrs? I'm unclear on how docs.rs is able to show which features are needed for an item.