.get() for full config, kwargs for export() YAML and JSON.

Currently, my json exports are unindented on a single line. This adds support for adding kwargs to include an indent.

kwargs in dumping pyyaml and json:

pyyaml.dump: http://pyyaml.org/wiki/PyYAMLDocumentation#Dumper
json.dump/dumps: http://docs.python.org/2/library/json.html#json.dump

``config.get()`` and ``.config.get('')`` return the whole config, equivalent to ``config.export('dict')``.