Removed documentation and download pages.  Website is being reorganized
around individual products.  We no longer have a single download
or single documentation page.
Navbar updated.  Selections are Products, Community, and Publications
Removed downloads folder
products folder created with webpages for 4 projects: diffpycmi,
pdfgetx3, pdfgui, and pythonpackages.

publications website created to track all publications coming
from diffpy project.
Redesign of diffpycmi and pdfgui product pages