Re-export namespaced enum variants

Enums in Rust are now namespaced.
To adapt to this without changing the API, we simply re-export the
enum variants where appropriate.

The goal is to fix the build.
The API can be changed later to properly make use of this new behavior,
if desired.
Merge pull request #61 from crumblingstatue/namespaced_enums

Re-export namespaced enum variants