allow a configurable collection instead of all HTML files
Merged in #4, released to v2.2.0

- v2.2.0 December 13, 2012
	- Added the ability to customise which collection is used
		- Thanks to [brockfanning](https://github.com/brockfanning) for [pull
request #4](https://github.com/docpad/docpad-plugin-sitemap/pull/4)