Ignore sublime text project files.
Basic functionality present

RGuard class returns a dictionary on ``__enter__`` which is then
saved to ``filename`` in json format on ``__exit__``.
Exceptions and non-JSON-serializable objects handled

Exceptions with traceback added to dict and suppressed (bad idea should change to reraise the exception)

Nonserializable objects are returned as strings, so the JSON encoding will not fail.