Remove a Knuth-added pun(?) from Witt's End.

Woods' message was
    YOU ARE AT WITT'S END.  PASSAGES LEAD OFF IN *ALL* DIRECTIONS.
Knuth changed it to
    You are at Witt's End.  Passages lead off in "all" directions.

The player might dismiss this punctuation as just another incorrect
use of "scare quotes" for "emphasis", but in fact I think Knuth may
have intended the quotes as a hint. Passages lead away from Witt's
End in all directions *except one*; hence not all directions, but
merely "all" directions. If so, this was a pretty clever little
modification, in the spirit of the original game.

However, in the interests of presenting a game as close to the
original as possible, I'm returning to Woods' wording.
Unfix some minor grammar corrections by Knuth.

Woods and Long both have "at top of stalactite"; Knuth has "on top
of stalactite".

Woods and Long have "a secret canyon which here runs E/W"; Knuth
has "a secret canyon, which here runs E/W".
ROAD and HILL are synonyms.

Yikes! This bug was introduced by me during my initial port of
Knuth's code; Knuth gets it right. I don't remember what I was
thinking. Anyway, I had mistakenly put ROAD and HILL as two
different motion-verbs, which meant that HILL never showed up
in the travel table and was therefore useless to the player.
They should be synonyms, such that typing HILL will take you
up (or down) the "hill in road".

This is now fixed.
Rearrange the motion vocabulary in original order.

Having the motion words in the same order as Woods' and Long's
will make it easier to showcase the differences between the two
versions, and also make it easier to verify that my list has
no unintentional differences from the original.

In fact my list *did* have an unintentional difference from
Knuth's; I was missing the synonym ASCEND for UP! This is now
fixed.
Rename CRYSTAL and BRIDGE to be more distinct.

Knuth's CRYSTAL is now FISSURE, and BRIDGE (the troll bridge) is
now CHASM. (CHASM isn't very distinctive, but I didn't like RICKETY
as an identifier.)

These identifiers match the names used by Woods, Long, and Platt,
and are already in use by my ODWY0550/. This also alleviates
ambiguity in "Adventure 6", which adds yet *another* chasm and
bridge (which is named CLAY) and a Crystal Palace (R_CRYSTAL)
unrelated to the crystal bridge.

No change in behavior.
Rename Woods' DOOR to RUSTY_DOOR.

Again to reduce differences required by "Adventure 6", which
adds three(!) more doors: a TINY_DOOR, a HUGE_DOOR, and a phone
BOOTH_DOOR.

No change in behavior.
Refactor is_treasure(t) and various objs(t).base references.

Woods cleverly puts all the treasures at the end of the list of
objects, so that "is this a treasure?" corresponds to "is this
object numbered greater than or equal to 50?". Knuth follows this
approach. But in "Adventure 6", we have too many new non-treasure
objects to keep following this approach, so Long introduced a new
object flag (bit 14) and function (TREASR) to distinguish
treasures from non-treasures. Let's switch to that approach.

One interesting thing about this change is that RUG_ is no longer
considered a "treasure", internally. This doesn't seem to have
any effect on gameplay. (I briefly wondered if looking at the
old rug from both sides would have given you 2+2 points instead
of just 2, but no, it doesn't.)

I've also cleaned up some other references to objs(t).base
while I'm at it. I don't think there's really any need to fix
the base of RUG_ before sending it off to R_LIMBO, and in
attempt_inventory() I don't think it's possible for the player
to be toting an immobile object.

Should be no change in behavior.
Compress the prop values of DRAGON and OYSTER.

The dead dragon had a prop value of 2 in Woods and Knuth;
I've compressed its values so that "dead dragon" is now
prop value 1.

I had warily set objs(OYSTER).desc[1] to NULL at the time
that I compressed a lot of the prop values and removed the
"Interesting. There appears..." message that had previously
lived there. However, I've now verified that objs(OYSTER).prop
never takes on any positive value, so we don't need this
assignment.
Rearrange the new_obj calls.

The object table initialization now happens in the same order as
in Woods' original data file, which is (not coincidentally) the same
order as their actual numerical values. This doesn't have any visible
effect, but it makes it easier to compare with the original.
Fix new_obj, and refactor try_move.

The new ordering of items means they get initially dropped
in the wrong order. So *that's* why Knuth assigned the numbers
mostly backwards from Woods' ordering! (And why his INVENTORY
routine counted down instead of up.)

Also, I've refactored the "try_move" code to more closely
match its layout in the original Fortran, to ease the
transition to Long's Adventure 6.
Rename Knuth's PONY to (vending) MACHINE.

Knuth explains in the literate comments that the identifier
PONY is a reference to the "Prancing Pony" at the Stanford
AI Lab (which was itself a reference to "Lord of the Rings").
However, this reference is original to Knuth; Woods' version
simply used the identifier VEND, and made no reference to
ponies, prancing or otherwise.

In the interest of not bewildering my readers, I've changed
PONY to MACHINE in all versions. (But I've left R_PONY alone,
because why not?)
Fix the "Adventurer Grandmaster" rank.

I was wrong in my comment in "adv550.c". Platt's "Adventurer
Grandmaster" is not a change from Woods (nor Long). Knuth's
"Adventure Grandmaster" is the variant. Good; I preferred
"Adventurer" anyway.
Fix some minor grammar issues in the intro and hints.

Knuth quietly changed "...is useful in discovering..."
to "useful for". This may or may not have been intentional.

Also, he intentionally spells out "commands of one or two
words" (versus Crowther's "OF 1 OR 2 WORDS"), which changes
the linebreaks throughout the rest of that paragraph. I don't
think it's worth the gratuitous difference, so I'm going back
to "1 or 2 words".

I've also changed Knuth's word "FORTRAN" to mixed case, which
is easier on the eyes (in case anyone actually reads all the
way to the end of the credits).
Bring into line with master commit 0073cc9c.

This revision includes minor tweaks to the initial help text;
the missing synonym ASCEND for UP; and the correct spelling of
the rank "Adventurer Grandmaster".