added json to picklemaps; added sync,open,drop methods to archives;
more unified __repr__ for archives and cache


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/pathos/klepto@606 8bfda07e-5b16-0410-ab1d-fd04ec2748df
Merge branch 'master' of https://github.com/uqfoundation/klepto