This library provides message digest functions found on BSD systems
either on their libc (NetBSD, OpenBSD) or libmd (FreeBSD, DragonflyBSD,
macOS, Solaris) libraries and lacking on others like GNU systems.

The intention here is to have a library with extremely permissive
licenses, that can be used by any project; that has a very small scope
and as such can be part of the base system on most distributions; and
that has a compatible API with the implementations on other systems and
those that other projects are embedding, so that they can switch to use
the system library instead of duplicating the same code all over the
place.