Throwable/Error.pm: Change POD, class is now built on Moo

I'd be more than happy to update the examples in the POD of all of the classes so they show either Moose or Moo being used with Throwable, but I'm not sure if that's desired, and if it is, what the best way to show both classes being able to consume the Throwable role.

If you do want to show both Moo and Moose being used, I could show two sets of examples, or maybe put comments behind the "use Moose;" lines to note that Moo would also work there too.  Or maybe something else?