inputLookup & outputLookup in to/fromJSON

Use boolean to indicate if inputLookup or outputLookup are necessary when saving to/fromJSON.

Avoids bug when training for output:{"0":1} gets interpreted as an Array when using fromJSON(net.toJSON())

Fixes https://github.com/harthur/brain/issues/22
Update json unit test
Will now use a "0" in input and output.
Merge pull request #23 from josher19/master

Handle cloned neural networks with a zero "0" in the output