Auto merge of #1733 - wackywendell:project-layout, r=steveklabnik

Auto merge of #1733 - wackywendell:project-layout, r=steveklabnik

I have several times found myself trying to remember where to put examples, and getting frustrated looking for it in the guide - because its not there, its in the manifest description, which I find to be a non-intuitive place for it. I thought it might help to unify the project layout sections between "The Guide" and "Manifest Description", and have them both link to each other for explanations where needed.

Of course, I am very willing to take any suggestions on my changes; I'm not wedded to any of text in specific, I just want the two sections to not be so separate and hard to find, especially from each other.