Add mirrors of POHL0000, DAIM0000, and HALL0000.

POHL0000 is mirrored from
http://cd.textfiles.com/pcsig13/PRO/DISK0259.ZIP
which appears identical to
http://cd.textfiles.com/pcsig08/201_300/DISK0259/

This is Jerry Pohl's 350-point "Adventure" (dated 12 JUNE 1984),
distributed by PC-SIG with the comment "Author Version: 03/90".
Its version information lists

        Conversion to BDS  C by J. R. Jaeger.
        Unix standardization by Jerry D. Pohl.

and no other authors.

DAIM0000 is mirrored from
http://www.ifarchive.org/if-archive/games/source/advtc2.zip

This is Daimler's 350-point "Adventure" (circa June 1990, according
to Russel Dalenberg). Its version information lists

        -Conversion to BDS  C by J. R. Jaeger
        -Unix standardization by Jerry D. Pohl.
        -OS/2 Conversion by Martin Heller
        -Conversion to TurboC 2.0 by Daimler

It contains Jerry Pohl's original ADVENT.DOC (dated 12 JUNE 1984),
plus comments from Martin Heller (dated 30-Aug-1988). Strangely for
an expansion, Daimler's version actually introduces a number of typos
into the data files, and disables a handful of inessential verbs
(READ, EAT, FILL) with the comment that there is "no room" for them
(presumably in the PC's limited memory).

HALL0000 is mirrored from
http://github.com/jncraton/minix3/commands/advent/

This is Robert R. Hall's 1994(?) port of MCDO0551 from Fortran to C.
It combines McDonald-and-Long's data files and Infocom-style parser
with the C framework iteratively refined by Jaeger, Pohl, et alia.
Its version information lists

        Conversion to BDS  C by J. R. Jaeger
        Unix standardization by Jerry D. Pohl.
        Upgraded to version 6.6 by Robert R. Hall.

The "Makefile" and "build" scripts are Hall's originals.
I'm planning to move them somewhere safe in the next commit,
so as to avoid people accidentally trashing their "/usr/bin/advent"
by running "make" in the wrong directory.
Unixify files in POHL0000, DAIM0000, HALL0000; add a Makefile for HALL0000.

Lowercase *.c and *.h in POHL0000 and DAIM0000.
Also replace DOS line endings (CR/LF) with normal line endings (LF only)
and remove the generated file "POHL0000/ADVTEXT.H".

The original versions of these files are available in the commit
immediately preceding this one. This change makes it easier to "diff"
the three versions against one another and see what Daimler added to
Pohl's version versus what Hall added.

Source information is now available in {POHL,DAIM,HALL}0000/README.