Register new package Dierckx

From the package README:

Julia library for 1-d and 2-d splines.

This is a Julia wrapper for the dierckx Fortran library, the same library underlying the spline classes in scipy.interpolate. Some of the functionality here overlaps with Grid.jl, a pure-Julia interpolation package. This package is intended to complement Grid.jl and to serve as a benchmark in cases of overlapping functionality.