Fix Lua 5.0 getn() crash on first guide load

GuideTable.lua:88 used the Lua 5.0 global getn() to size the color-
substitution table opentext. In Lua 5.1 (WoW 3.3.5) the bare getn is
gone and table.getn is deprecated, so this would have crashed with
'attempt to call global getn (a nil value)' before any guide could
render. Replaced with the # length operator.

Also record the fix and the upstream README cleanup under 'Files we
touched' in README-CoA.md.

GuideTable.lua

@@ -85,7 +85,7 @@ function objGuideTable:new(oSettings)
 								["replace"] = "|c00a80000"
 							},
 						}
-						for n = 1, getn(opentext) do
+						for n = 1, #opentext do
 							t1[k1].items[k2].str = gsub(t1[k1].items[k2].str, opentext[n]["find"],opentext[n]["replace"])
 						end
 						t1[k1].items[k2].str = gsub(t1[k1].items[k2].str, "#","|r")