Use the OES_texture_float extension if available

[flash1293]

The OES_texture_float extension makes it possible to specify a texture with float pixels. This means a float32 array can be directly used.

By using this the pack/unpack functions can be omitted, possibly speeding up reading/writing to arrays in the shaders.

https://developer.mozilla.org/de/docs/Web/API/OES_texture_float

[VictorTaelin]

I'm aware of the extension, but I didn't manage to get it to work properly, for reasons I sadly don't remember. Maybe I can try again eventually. I feel like this needs a better documentation, or at least some examples...