Make cfpropertylist the default

Previously, I had made rubycocoa the default provider for the rubycocoa
feature, and the same for cfpropertylist. The problem would arise where
you could have BOTH libraries installed, and both would be listed as the
default provider. Since Rubycocoa is effectively dead, I'm making cfpropertylist
the default from here-on-out.
Merge pull request #16 from glarizza/cfp_default

Make cfpropertylist the default