Added abbreviations for publications using DiffPy-CMI.
Also added links to online versions of publications where available.
Updated installation instructions.  Creating a symlink to diffpy_cmi.pth
is no longer necessary if one runs the install script.
Revert to the original logo.
Add spacing around CMI button, replace ackno --> Credits.
libobjcryst is external library.
Shorten license reference so it fits on one line.
On MacPorts use gsl instead of gsl-devel.

gsl-devel is not maintained, gsl package is.
Reformat and expand on MacPorts.

Add diffpy-dev link for installation help queries.
Link to the latest DiffPy-CMI release bundle.

No need to update this later.
Fix broken links or replace with citation URLs.
WIP - sort out italic links.