Add support for ujson to storage plugin
Add support for ujson to storage plugin

This commit adds automatic support for [ujson](https://pypi.python.org/pypi/ujson), a faster json implementation than the Python default. If ujson is installed in the user's site packages, it will automatically be imported as `json`, so no other code changes are necessary to benefit from it.
mrhanky17/irc3,mrhanky17/irc3,gawel/irc3