[Ifeffit] Generating single scattering paths in Artemis

[Matt Newville]

Hi, 

It doesn't seem that hard to have a procedure to auto-generate and
run Feff6 with a rock-salt or simple tetrahedral environment,
either in Artemis or a standalone application -- I'd vote for
emulating Sam's approach in Artemis.  I strongly agree that no one
should be expected to use Rydbergs or the OVERLAP card, or even
know that Feff has an input using things called 'cards'.

I'd prefer it if the running of Feff was a little more modular,
and a little less tied to Artemis, but a decent Feff GUI is
probably a separate topic.

Another approach would be to recognize that the results of a SS
Feff calculation can be stored in ~3kb, so it's not unreasonable
to think about making tables of pre-calculated SS paths for nearly
all reasonably likely SS paths.  It might also be nice to have
these in a network-accessible database so that it wouldn't always
be necessary to calculate SS paths or store a huge table of them.

--Matt