Consider replacing the bindgen-generated bindings

the MFX API uses way too many unions and bindgen seems to make a lot of confusion and anonymous fields that you might have problems to access if the bindgen changes.

*PROS*:
- Nicer low level abstraction

*CONS*:
- Lots of work

*NEUTRAL*:
- hand made bindings require to be updated manually
- auto-generated bindings might break suddenly because how the api is currently mapped anyway.