Added XC example to wikibooks "Hello World!" page.

[Heater]

I noticed that no one had added the XC language to the wikibooks page of "Hello World!" programs. So I took the liberty of doing so. http://en.wikibooks.org/w/index.php?tit ... table=0#XC

It's a bit of a long hello world but I wanted to show off some XC features, otherwise it would just look like C.

If anyone has any improvements, well it's there for the editing.