datetime review part 2 [Update 3]

[Jonathan M Davis]

Newest version: http://is.gd/gHy43

Small update. I found a bug in the fromXString() functions for SysTime that I 
hadn't managed to test for (the appropriate tests have been added), and in using 
the module, I found that it was highly annoying to have to type out UTC.instance 
to get at UTC's singleton (it's just too verbose), so I changed UTC.instance and 
LocalTime.instance to static opCall(), so you write UTC() and LocalTime() 
instead. It seems more pleasant that way (though part of me wishes that the 
class name alone would be sufficient...).

- Jonathan M Davis