Rename ddc::BoundCond #1063
Description
The enum ddc::BoundCond is poorly named which can lead to confusion. In the context of spline interpolation the provided methods are not boundary conditions but rather closure conditions. Closure conditions are conditions which provide additional information in order to complete the definition of the system. This extra information may or may not be found at the boundary. For example ddc::BoundCond::GREVILLE (which is also poorly named) imposes that the number of interpolation points is equal to the number of basis functions. The additional points required to achieve this do not need to be placed at or near the boundary (or at Greville abicissae).