Provide conveniences around converting Numpy arrays to/from Javascript typed arrays

[mdboom]

Currently, you can pass a typed array to Python, getting a buffer which you can then use with np.frombuffer to get a Numpy array (and make sure you match the datatype on both sides). When passing a Numpy array to Javascript, you get regular (non-typed) Javascript arrays, which is a less-than-optimal use of memory. This requires getting the datatype correct and knowing how to do this.

It would be nice to have a more convenient way to do this. It can't be built-in, since the user may not be using Numpy, but maybe if there's an explicit way to turn this on, the conversion code could then implicitly do this.