Rename `labeled()` to `named()`
Rename some internal variables and methods.
Merge pull request #85 from cgruber/renamelabeled

Rename `labeled()` to `named()`
Add support for a custom message (plus tests for the same)
Merge pull request #86 from cgruber/withFailureMessage

Add support for a custom message (plus tests for the same)
Add a subject for Guava's Optional.
Add hasValue() to OptionalSubject
Fix error names a bit.
Fix up some javadocs.
Fix copyrights and generics in TestVerb.
Improve the messaging on a null-subject passed in to OptionalSubject
Add OptionalSubject to GWT