redo the currying syntax to get rid of one of the arrayrefs

redo the currying syntax to get rid of one of the arrayrefs

this will make it more difficult to add things like the subref form of
currying in the future, but it is simpler and cleaner for the vastly
more common case, and the subref form could be added back in via
something like handles => { foo => { grep => sub { ... } } } (rather
than using [] for the middle pair of braces, which would continue to
mean normal currying) if we decide it's really necessary.