Add fieldName as first parameter to Bind and Binder.

I cherry-picked `66f260ce1bae688e36a3392d6b3ee9efc4bce6aa` from @wmark to implement his fix for passing the field name to `Binder.Bind(...)` as requested in #9.

It applied cleanly, and I didn't run any testing, though; I assume @wmark can handle creating the tests.