Time.parse is documented in ri, but doesn't seem to be defined. Do I 
need to require something from the stdlib?

I'm looking for an easy way to convert things like "4:30" to relative 
values--seconds since "00:00:00". I can just parse manually, of course, 
but was hoping for a standard way to do it, like

Time.parse("4:30") - Time.parse("0:00")