making page generator work for different libraries

Page Generator was hard coded to work with the Microsoft.AspNet.Diagnostics library only. This change allows you to give a different library to generate pages.
Stuff that's still hard coded - the generated files will use the BaseView in the Diagnostics library, and the files being generated must exist inside a "Views" folder within the library.

@rowanmiller Chris told me you were also working with this - do you need it to be more flexible?