Add OpenBSD support
Merge pull request #17 from jasperla/openbsd

Add OpenBSD support
Update to 2.3.2
Extract structure creation code into a method.
Fix up issue with shadow implementation.

When the implementations were split into shadow and pwd, the code
initialzing the structure used in the shadow implementation was replaced
by older code not including the added field, always nil in that
implemenation, for pw_change.

The intent currently is that the passwdEntry structure should contain
all the fields available across implementations.
Document fields better.
Change name to match name used in pwd/shadow.c
Move location of function.
Bump version.
Update history.
Support MirBSD and NetBSD, like FreeBSD and OpenBSD.

Also simplify the table in the readme file; the supported set of
features is the same for all BSDs.
Remove requirement for getpwnam_r.

The function is never called. MirBSD does not have it.
Merge pull request #20 from bsiegert/master

MirBSD and NetBSD support
Bump verison.