binding-go: support multi-dimensional observations

[unixpickle]

This is useful for environments like Atari, where observations are 3D tensors. Before now, multi-dimensional observations would yield an error. This commit also comes with a new demo that showcases how to use 3D observations in Pong-v0.

This replaces #47 which achieves the same result but in a less general way.

Informal benchmarks show that using reflection for multi-dimensional observations, like is done here, does not negatively impact performance. Processing space elements for pong took roughly 0.2ms per frame on a 2.6GHz Core i7.

[wenkesj]

@korymath looks good to us Go coders here 👍

[joeblew99]

Would be great if this was committed please.

I have a parametric CAD system written in golang. With it i can design 3d objects and the 3D robots to make the objects, but using the golang vncdriver and some tensors. But i need to hook into the "gym" to get some help....

[joeblew99]

thanks !