standarize documentation (and indirectly code) to use American English as discussed in 4f234bfd

Please do not perform monster patches for this until 3.1 is out.
Also, no existing API should be affected by this. New code, local
variables, etc. would follow this guideline to have a consistent
project tree in this regard.

railties/guides/source/api_documentation_guidelines.textile

@@ -33,6 +33,10 @@ Spell names correctly: Arel, Test::Unit, RSpec, HTML, MySQL, JavaScript, ERB. Wh
 
 Use the article "an" for "SQL", as in "an SQL statement". Also "an SQLite database".
 
+h3. English
+
+Please use American English (_color_, _center_, _modularize_, etc.). See "a list of American and British English spelling differences here":http://en.wikipedia.org/wiki/American_and_British_English_spelling_differences.
+
 h3. Example Code
 
 Choose meaningful examples that depict and cover the basics as well as interesting points or gotchas.