Extracting example dependencies to `extra_require`

[cloderic]

It is possible to install the package directly from GitHub which simplifies a lot using it with a pip install https://github.com/kenjyoung/MinAtar.git (I'm actually doing it with poetry with a poetry add git+https://github.com/kenjyoung/MinAtar.git but that's mostly equivalent).

However because of the way the setup.py is written this also installs the dependencies for the examples (especially torch which is a behemoth). Would you consider removing them ?

A way to do it simply would be to create an extra section to group the examples dependencies, something like:

extras_require = {
     'examples':  ["torch"]
 }

I could contribute the change if you think it makes sense.

[kenjyoung]

Yes, this makes sense to me, feel free to make a PR.

[cloderic]

Done!

I can confirm that it solves my problem when installing from git and that it works as before when installing locally if you specify the examples extra -> pip install ".[examples]"

Let me know if something needs to be changed

[kenjyoung]

Looks good, thanks!