Redundancy in coil spline parametrization

[jbreslau]

The present implementation of coil splines in STELLOPT makes use of a a pair of arrays for each dimension, e.g. COIL_SPLINESX and COIL_SPLINEFX giving the values of the spline parameter s and the value of x(s) respectively for each knot. Neil has pointed out that it would make more sense to have a single s parameter for all dimensions, i.e. a single COIL_SPLINES array giving the s values, and then (x,y,z) triplets or (u,v) pairs giving the actual coordinates at each s value specified by the usual COIL_SPLINEFX, ...FY, ...FZ arrays.

If this makes sense to everyone, it could be achieved without sacrificing backward compatibility with the use of an EQUIVALENCE statement, effectively aliasing the new COIL_SPLINES array to the three previous ones.