Some cleaning of PDFgui page.
Update installation instructions for DiffPy-CMI to include zsh, git, and
scons as dependencies.

Added instructions for installing dependencies in Fedora.
Updates to diffpycmi pages.

documentation renamed contents (documentation links are now on
index.html)

cmi_exchange page updated to include additional instructions for users.

pythonpackages page updated to include all DiffPy packages.
Merge branch 'source' of https://github.com/diffpy/diffpy.github.io into source