Separate gallery examples out into new diagrams-examples package

[fryguybob]

(Imported from http://code.google.com/p/diagrams/issues/detail?id=69. Original issue from [email protected] on March 5, 2012, 09:38:06 PM UTC)

This will probably have to wait until the SVG backend is done, so we can make diagrams-examples depend on it and give people an easy way to quickly get their hands on some working examples. The idea would be for this package to contain source (with included commentary) for a bunch of examples, along with an easy way to build them all. We would also want a way to auto-populate the web gallery from this package.