Exposing checkInitialized for input sanitation

[joshbuddy]

First thank you for this excellent library!

I wanted to discuss making an API change. Specifically the checkInitialized function would be useful to have exported to make it easier to sanitize inputs. How would you feel about exposing that function? If that makes sense to you I'm happy to provide a pr.

[FiloSottile]

What kind of input sanitization do you need to do? checkInitialized exists only to catch API misuses where zero-valued Points are used as inputs.