CoordInterpGrid: specify location and scale of coordinates

[simonbyrne]

This adds the ability to specify location and scale of an interpolation: see discussion on mailing list.

One-dimensional usage simply requires specifying the range as first argument:

x = -1.0:0.1:1.0
z = sin(x)

cg = CoordInterpGrid(x,z,BCnil,InterpQuadratic)

Multi-dimensional the ranges are specified as a tuple

cg = CoordInterpGrid((x,y),z,BCnil,InterpQuadratic)

Gradient calculations are also supported via valgrad.

[timholy]

First-rate work, @simonbyrne. Many thanks!