Remove gratuitous keyword arguments.

1. The only implementation that officially does keyword arguments is MRI
   2.x.  (Maybe JRuby does.)
2. I'd like to try other Ruby implementations to see if they behave any
   better under load.
3. Wanting (2) means that we need to stick with a Ruby 1.9-ish feature
   set.  This means no keyword arguments.
4. We really don't use the flexibility of keyword arguments in
   ArchiveUrl anyway.