Registry Classes, Including, Named Instances Docs

Here's my first take for the Registry DSL docs. They're heavily inspired from the [old docs][old], but with snippets from real tests. Since other snippets were checked in, I added these, but it doesn't seem like they need to be there with the `fubudocs` command automatically pulling snippets in. I'm happy to go with either approach.

I did update the tests to replace blank lines with comments, because for some reason my browser showed any snippets with blank lines like this:
![tests-with-spaces](https://cloud.githubusercontent.com/assets/230004/2587214/19706c34-ba18-11e3-8d03-d8c9897d9ed3.PNG)



[old]: http://docs.structuremap.net/RegistryDSL.htm