More tests!

[leeper]

• [x] `%unf% equivalence operator

• [x] print method

• [x] dispatch to old versions (3, 4, 4.1, 5, error otherwise)

• [x] raw vectors:

  Normalize bit fields by converting to big-endian form, truncating all leading empty bits, aligning to a byte boundary by padding with leading zero bits, and base64 encoding to form a character string representation.

• [x] dates

• [ ] datetimes

• [x] difftimes

• [ ] character encoding

Note: some of these are carried forward from #2.