feffpath + wrapper

I made it!  I now have a comprehensive and useful tool for generating individual paths given a scattering geometry.  There is a Fortran entry point (libonepath.a) and a C wrapper around that (libfeffpath.c).  As a proof of principle, I made a fairly simple Perl wrapper using SWIG.

I have also improved upon the build system so that it now installs to a sensible location, albeit only on a linux machine.  The build scripts will need work for Windows or the Mac.

For now, cd-ing to the `src` folder and doing

       ~> scons
       ~> scons install

will compile everything, install the various stand-alone "modules" to `/usr/local/bin`, and install various static libraries to `/usr/local/lib`.  The static libraries include `libonepath,a` and `libfeffpath.a` as well as libraries for all the various parts of feff (with names like `libfeffmath.a` and `libfeffatom.a` to avoid name collisions with other packages).

If SWIG is installed, the `scons` step will generate the various SWIG files for the perl wrapper.  Then the `scons install` step will copy them into the `wrappers/perl` folder so that the Perl wrapper can be built using Perl's normal build tools.

The next steps are to write good documentation for everything and to incorporate individual paths into the overall unit testing framework.