Add binary transport

[xhluca]

Binary transport will potentially lower the size of the arrays being passed to JS, and might speed up the process as well.

How we could implement it: Given a numpy array, we compute the shape, the dtype, the b64 encoded memory view of the flattened numpy array. Then those three values are passed as a dict/json to the frontend, which is then reconstructed into a typedarray. The plan would be to use this function on the python side.

For more information, see this pull request as well as plotly/plotly.py#2943

[jourdain]

Done in #43