[DELETE ME] Added README.md note about branch rewriting

This commit should *not* be merged into master; remove it before merging.
Validation warnings now stored in state object

This will allow for additional processing before actually triggering the
warnings. For the sake of this commit, though, we just keep with existing
functionality.
Began implementing virtual trait methods

N.B. This is incomplete, as the test case is throwing a warning (see the
incomplete test for a description of what needs to be done). This commit
will likely be rewritten.

These require special treatment with proxying.