Rust OpenCV bindings

This is my shot at generating Rust bindings for OpenCV.

This is absolutely not ready for prime time.

Instead of binding the deprecated C-compatible interface, I chose to mimick the python and java wrappers: parsing C++ headers, generating a C interface to the C++ api, and wrapping this in Rust.

Current progress, notes and todo list

Stuff that work (with examples):

• video capture
• conversions
• orb detection (and probably description too)

Notes for my later self:

• Are there any other modules that should be added to the list ? Can I disco them ?
• Working with cv 2 here. What about version 3 ?
• Safe high-level Rust interface could be nicer
• No tests
• Discovered some troublesome types in flann. They do not conform to cv convention, so I think I'll just wrap them by hand and feedback their existence somehow to the generator.