Draft: ENH: default to json load for dictionaries and lists from strings

See #287

This MR adds a default attempt to use json to load the inputs, any failures will simply pass down into the old behaviour.

If we have this in, any new requests for more complex parsing, we can refer to here and require that they follow json, instead of making our logic increasingly confusing.

I also added a mechanism to easily turn on enforcing json inputs to these functions a la np.errstate if we want to make json-formatting required.