Created a very basic initial target function class for relaxation dispersion.
This code is a translation of Sebastien Morin's C code in the old relax_disp branch. This old code
can be checked out with the commands:
$ svn co http://svn.gna.org/svn/relax/branches/relax_disp/maths_fns/relax_disp.c@r18123
$ svn co http://svn.gna.org/svn/relax/branches/relax_disp/maths_fns/relax_disp.h@r18123
