* Migrate portable functions from GNU/kFreeBSD's libfreebsd.
* Add more functions used by ported packages (check openssh).
* Add more unit tests.
* Add missing man pages.
  - bsd_getopt.
  - timeconv?
* Add a README.import file.
* Update man pages:
  - Document when each interface was added on every BSD, and libbsd.
* Handle LFS properly. By default the library emits LFS objects, but might
  be used by non-LFS objects. We should either provide foo and foo64
  functions and appropriate mappings on _FILE_OFFSET_BITS=64,
  _LARGEFILE_SOURCE and _LARGEFILE64_SOURCE. Or error out when the off_t
  used by the code including us does not match a 64-bit type.