Add support for buffer usage flags

[DomWilliams0]

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At the moment it looks likeall OpenGL buffers are hardcoded to use GL_STREAM_DRAW. It would be nice to be able to customize this per buffer to use GL_DYNAMIC_DRAW etc.

Thank you!

[hadronized]

What is your current need for this?

[DomWilliams0]

Nothing currently, I was just looking through the API to assess it for my needs. It's very minor though as it's just an optimisation hint