Add object_hook option to unpack and default option to pack.

(see simplejson for how to use).

test/test_obj.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+# coding: utf-8
+
+from nose import main
+from nose.tools import *
+
+from msgpack import packs, unpacks
+
+def _decode_complex(obj):
+    if '__complex__' in obj:
+        return complex(obj['real'], obj['imag'])
+    return obj
+
+def _encode_complex(obj):
+    if isinstance(obj, complex):
+        return {'__complex__': True, 'real': 1, 'imag': 2}
+    return obj
+
+def test_encode_hook():
+    packed = packs([3, 1+2j], default=_encode_complex)
+    unpacked = unpacks(packed)
+    eq_(unpacked[1], {'__complex__': True, 'real': 1, 'imag': 2})
+
+def test_decode_hook():
+    packed = packs([3, {'__complex__': True, 'real': 1, 'imag': 2}])
+    unpacked = unpacks(packed, object_hook=_decode_complex)
+    eq_(unpacked[1], 1+2j)
+
+if __name__ == '__main__':
+    #main()
+    test_decode_hook()