[Checkers] New material for checkers paper

[Matt Papi]

I am available any time tomorrow.

>  > If there is anything new that you know of that could go in the
>  > checkers paper, please let me know.

- framework meta-annotations (manual section 8.5.1)
- polymorphism (not done yet, will be in SVN in the next couple of
days; can actually be part of the meta-annotations discussion, since
it's done via a @Polymorphic meta-annotation)
- nonnull @Raw types (manual section 3.3)
- custom checker (manual section 8.1)


- Matt