Expose pandas.json.dump in the public API?
I could not find any public documentation for `pandas.json.dump`, so I guess this makes it private? Or is it public and I can depend on it?

Would you consider making this function public, or at least as public as `pandas.json.dumps` which are at least imported into/as `pandas.io.json.dumps`. 

I find the performance of `pandas.json.dump` to be an improvement on the normal json module.
