[Ifeffit] A potentially useful feature in Artemis

[Matthew Marcus]

As it is now, if you want to describe your unknown structure as a distorted version of the one for which FEFF was run, you have
to enter formulas for distances by hand.  For instance, suppose you're doing a substitutional dopant and you want to use Artemis to
fit the displacement of the impurity off-site and the dilation/contraction of the first-neighbor shell.  As it is now, you have to
do the algebra yourself to compute all the distances in terms of the distortion parameters.  It would be really nice if there were
some syntax for describing the alteration of atom positions, from which Artemis would automatically compute the displacements.  This might
have to be a new class of parameters.  Such a computation would cover the MS paths as well.  What it would still NOT do is account for
the effect of leg-to-leg angles on MS paths (deviation from focusing/backscatter), but it would be a step.  I realize that this would be
a big job to implement in a nice way that wouldn't break everything that came before, but it would be super useful and make the IFEFFIT team
(yet again) heros to the community.
	mam