#8 algorithm for cubic spline interpolation of complex 1D array

[van den Bosch]

This patch allows for the interpolation of 1D complex
arrays by means of cubic splines. The abscissaes of the
array must be real. It contains 4 programs:
- spline_f2 : which computes the second derivatives of
f at each ascissa x
- splinterp1D_point : which interpolates f at the real
abscissa x_i
- splinterp1D_array : which interpolates f at the real
array of abscissa x_i

These three programs are grouped in "splinterp1D.cpp"
and "splinterp1D.h". The natural condition (i.e. f2 (0)
= f2(toEnd) = 0.0) at both ends is assumed. The
extension to allow user to choose f2 or f1 at both ends
is straightforward, and will be done if needed.

- test_interp.cpp : a simple routine for testing the
interpolation. One can easily change the function
generating the array.

[van den Bosch]

[van den Bosch]

[Sylwester Arabas]

Migrated to github: https://github.com/blitzpp/blitz/issues/86