If none of the HH2_*() macros are used, the binary will show up as its
own filename instead of random garbage.
If HH2_NAME() is used the metadata will be read, and the binary format
requires that all fields by specified. Using only a subset of the macros
is invalid, but not reported.
Features will come in slowly while I restructure for gint 3. With this
third big target for gint, the legacy aspects of gint 2's structure and
API are getting felt, so a major revision will be in order.
See the TODO file at this commit for info on what works and not.
