TODO
====

	* Written documentation in the form of a vignette. - DONE in 0.5-0
		
	* A formula method for 'mat' - DONE in 0.3-4
	
	* Thorough code review, testing and consistency
	checking - this will be the first widely
	advertised release.
	
	* Need to consistently have functions store DC Method as an 
	attribute. Good to write an extractor function and have all
	functions use that.

	* Speed-up distance() - move it to C
