Add support for 'ADR' field.
TODO: Also handle 'LABEL' field (which lives inside 'ADR' in vC 3.0+)
Several changes to support vCard 2.1 files as best as we can.

Inculdes support for reading multiline quoted-printables.
TODO: Refactor for readability, and actually decode the QPs.

Unknown attributes are inferred to be 'TYPE' -- if we want to do this
rigorously, we can validate more thoroughly against the spec.
Section 10.3.4 of the RFC gives valid values for 'TYPE'