PR: Convert array_object.md to rst

[steff456]

This PR converts the array object markdown into rst

Ref: #283

Note: It seems that the circleci redirector action only works if I open the PR from my own master branch. Given that I'm opening multiple PRs from branches, I'll update the link for the preview manually for each.
Preview: https://38-335160819-gh.circle-artifacts.com/0/build/latest/index.html

[asmeurer]

I think the main question here is if we're OK with the notes in the various functions being replaced from note directives, which render as blue "Note" boxes (see for instance https://data-apis.org/array-api/latest/API_specification/array_object.html#floordiv-self-other) with a simple "notes" section, which is how numpydoc renders the Notes section. One downside is that notes no longer appear next to a specific part of the docstring. They only appear together in the notes section.

If we're fine with this, I only have the one minor comment about a formatting issue. If not, we should change the "Notes" sections to use .. note:: directives to match the way it currently looks in the Markdown. @rgommers @kgryte any thoughts?

[steff456]

Just as a clarification, at the end I decided to compress all the notes in just one section because as we are using Numpy style documentation I'm unable to call the .. note:: directive inside the docstrings. I've been researching, and I think the closest I can get is to activate one option in napoleon which will render the notes in a box as before, but I think I still cannot create one admonition for each one.

Edit: I found a way to do it 🎉 and updated this in the last commit

[asmeurer]

Great. This looks good now.