Implemented a metaclass-based technique for self-registering handlers

--HG--
extra : rebase_source : d301524fd9a0d799ea0344508e675ea9c93f170f
Use self-registering handlers for Datetime objects
Merge pull request #41 from jaraco/self-registering-handlers

Self registering handlers
pickler: remove unused import

Signed-off-by: David Aguilar <davvid@gmail.com>
util: avoid calling repr() in is_type()

repr() can be an expensive operation, and can be tickled into an
infinite loop when external code uses jsonpickle in its repr()
implementation.

Avoid the problem entirely by checking the type against types.ClassType,
which is simpler and more robust.

Closes #23

Reported-by: Todd Kennedy (@toddself) <todd.kennedy@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>