add example: fitCdSeNP
add .settings (generated by eclipse) to .gitignore
Changed the markers for plotting experimental data.
Merge branch 'master' of https://github.com/diffpy/cmi_exchange
none fill color should be better than white
Demo the Bond Valence Sum calculator.

Example calculation for NaCl and optional customization of
bond valence parameters.
Update installation instructions for cmi_plugins.
Remove the obsolete install_ext instructions.

The URL was wrong and install_ext is careless enough not to notice.
Including own URLs in source files is bound to get wrong soon.
Let's not do that.

install_ext is also bad choice for every updates in the cmi_exchange
repo would have to be installed separately.
Fix forgotten quote, join the second paragraph.
Avoid excessive GitHub links.