Bump version number to 0.4 dev.
Bump version number to 0.4 dev.

Use "dev" tag to distinguish from official release.

mandx/jsonpickle,dongguangming/jsonpickle,dongguangming/jsonpickle,dongguangming/jsonpickle,mandx/jsonpickle,mandx/jsonpickle,dongguangming/jsonpickle,mandx/jsonpickle