docs for anatomy of an Atlas chart

[brharrington]

The request was something like:

http://home.gna.org/pychart/doc/anatomy.html

That was cross linked with other parts of the docs. This would make it easier for a user to quickly find the examples and options that control a particular aspect of the chart. Can also be a good quick reference for new users that are not familiar with some concepts like the SI prefixes used with the units.