We need to document the test coverage.

I have pushed a page tests-coverage.md to master and enabled GitHub Pages so that it shows at https://data-apis.org/array-api-tests/tests-coverage.html (it also created a page for the README). I started a basic table with statistical functions, based on #39. It's not yet completely filled out.

@honno Let me know what you think of the general styling and the categories. My thinking is each cell will have "Yes", "No", or "N/A", and if there is more to say about something we can add a footnote. The idea is based on tables you often see on Wikipedia (e.g., this one).

Feel free to edit it and to fill it out more. You can push directly to master if you want. I don't know if there is any other way to see a preview of the page without pushing to master and letting GitHub render it. You can also change the theme if you want (see https://github.com/data-apis/array-api-tests/settings/pages). I was also thinking of adding some Javascript that colors the cells green if they have "Yes" in them and red otherwise.

By the way, if you use emacs, the markdown-mode makes it really easy to edit the table. You can just press tab and enter to move between cells, and it automatically realigns them. I don't know if there are similar plugins for other editors.