feff8l exe distributed with demeter

[newville]

great interest from Q2XAFS 2017 for Feff8l development, but a good request that executables for feff8l should be included with Demeter

It might be reasonable to simply copy and include the executables for Win32, Win64, and Darwin from https://github.com/xraypy/xraylarch/tree/master/exes

Actually, for the Mac OSX distribution, it will probably be necessary to alter the executables to point to the Fortran dynamic libs. I can provide a script to do this, but it may need to be coordinated with the MacPorts distribution.

[bruceravel]

Good to hear. Defaulting to feff8l in Demeter will require a bit of work, but it is quite reasonable to do that for the next release.