Minor variable name change (for clarity)
(#432)
Fix doc re conserve_flux parameter
(#432)
Switch test_spline tests to use InterpolatedImage rather than SBInterpolatedImage
(#432)
Move the non-trivial functions out of Interpolant.h and into Interpolant.cpp
(#432)
Change Lanczos variable in C++ to conserve_flux to match python variable name.
(#432)
Use direct calculation for Cubic and Quintic uvals as well.  (Plus some Geekery about deriving the polynomial interpolants along with an alternate Quintic formula with different properties, and the formulae for Septimic if we ever decide we need it.)
(#432)
Implement more accurate Si function
(#432)