Add a function to calculate Bezier spline

[fatcerberus]

Not to draw one, just to calculate points along the curve. That's useful not just for graphics, but in other applications as well, like tweening.

[fatcerberus]

Open question is whether this should be limited to cubic curves, or make it work with any number of points. I’m leaning toward the latter; especially if this is going to be part of the Core API, it needs to be as flexible as possible.

[fatcerberus]

I think it makes most sense for this just to do cubic splines, as that's the most common scenario.

[fatcerberus]

Pushing this back to miniSphere 5.0; 4.8.0 release is only a few days away and I haven't decided where this fits into the API yet, so I'm postponing it.

[fatcerberus]

Removing the milestone until I can think of a good, extensibility-friendly way to slot this into the API. With an API freeze coming up in miniSphere 5.0, any new API categories will need more thought than in the past, to ensure future extensibility without the need to break compatibility.