v0.2.0 BSpline Rework

This release mostly fixes and reworks aspects of the BSpline type.
The constructor is now way stricter and won't allow building BSplines from invalid parameters.
Some errors regarding knot spans and evaluation have been fixed, unclamped BSplines should now also function properly.

List of main changes:

1. New enum BSplineError to communicate invalid parameters
2. New enum KnotVectorKind to distinguish between clamped and unclamped splines
3. knot_domain() is now specialized and should handle both cases correctly
4. Fixed Cox-DeBoor evaluation off-by-one errors for some BSpline configurations