We'll continue to favor simpler data models that can be
used directly rather than wasting time and memory with
accessor APIs.
The ->from, ->to, -cc, ->mid, ->subject, >references methods can
all be trivially replaced by hash lookups since all their values
are stored in doc_data. Most remaining callers of those methods
were test cases, anyways.
->from_name is only used in the PSGI code, so we can just
use ->psgi_cull to take care of populating the {from_name}
field.