[Docs] Document most scheduling functions.

[jku20]

Description

Documents the functions exposed by the scheduling language and by the dsl.

Problems

Documentation (or the lack thereof).

Proposed Solutions

Added documentation.

Examples

N/A

Checklist

• PR's title starts with a category (e.g. [Bugfix], [IR], [Builder], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage (It would be better to provide ~2 different test cases to test the robustness of your code)
• Code is well-documented

[chhzh123]

Hi @jku20, thanks for your contribution! This is really helpful! Could you follow this guide to format your files before I take a closer look?
https://cornell-zhang.github.io/allo/developer/index.html#id1

[jku20]

Of course! I'll un-draft this PR and request a review when it is ready (it should pass all the CI formatting, and non-formatting for that matter, checks then too). At current, this is just the quick, lightly edited copy-past of the scheduling functions.

[jku20]

I haven't got around to doing the functions in the dsl, but here is reasonably usable, though not really complete, documentation of the scheduling functions and types.

[jku20]

The above PR should be functional (whatever that means for docs). Do double check it though as I'm not 100% confident on everything.

Especially check the documentation of to. I couldn't figure out what axis was doing (or what depth=-1 means) so I just copied the docs from the tablegen of the op the thing schedule gets lowered to.