stdlib.h: add all C89 stuff

libnc.3: add a little section on standard versions

libnc.3: use non-breaking space in a few places

I wish v7 troff had \~.  Is there not maybe some kinda trick to get
paddable non-breaking space with v7 troff?

stddef.h: expose things only for their C version

stddef.h: declare ISO C and POSIX stuff

stdio.h: add POSIX stuff

define NULL in stdio.h

don't expose prohibited identifiers in headers

ISO C doesn't allow you to declare identifiers ending in _t in any
header you want, other than POSIX.

add Makefile

just for building for now, not for installing

add LANGUAGE, README, TODO

libnc.3: add implementation-defined behavior

stdio.h: declare all the ISO C stuff

sys/cdefs.h: remove annoying extra blank line

assert.h: don't use __const in prototypes

make header guard names short enough

Unix v7 cc only cares for the first eight bytes of the name.
_LIBNC_STDIO_H and _LIBNC_STDDEF_H aren't that different, it seems.

add a few headers, sparsely filled

and an implementation of assert