Standardize on American spellings.

Full internationalization would be much cooler, but that's never going
to happen.  Given that, this will at least prevent folks from constantly
having to look and switch between typing "armor" and "armour", depending
on which zone each item originated in, etc.

I could flip these either way, but a survey of the current state shows
that about 80% of the mixed cases use the American spellings, while 20%
use the British.  And, most words *only* exist in this data in their
American forms.  So, it seems the majority prefer these spellings.

In case anyone likes trivia:
* The most common mixed words in here were "armour" and "colour", each of
  which occured about half as often as "armor" and "color", respectively.
* The most British word in here was "theatre" (including other forms),
  which occured about twice as often as "theater".

This stanardizes all of these (and other forms of these same words):
* armour -> armor
* colour -> color
* favour -> favor
* honour -> honor
* civilise -> civilize
* centre -> center
* theatre -> theater
* defence -> defense
* offence -> offense
* realise -> realize

lib/world/wld/101.wld

@@ -402,7 +402,7 @@ S
 The South Road~
    You are walking along the south road connecting the city to the north with
 Haven to the south.  The road is bustling with activity as travelers are going
-to and from the city which is considered to be the centre of the world around
+to and from the city which is considered to be the center of the world around
 these parts.  A gust of warm wind blows in from the east, as if to remind you of
 the desert not too far off.  You see fertile grasslands to the east and west
 while the road itself continues to the north and south.  Just south of here you