Document warning numbers

[Minnozz]

Fixes #190

[ryyppy]

This looks generally pretty good.

A few things:

• Not sure if we should call the sidebar navigation item Compiler Warnings... sounds more like an FAQ collection of error messages (problem -> solution). Maybe Warning Numbers would be better?
• I noticed that our Warnings collection has deviated from upstream (still a bunch of BuckleScript words in there). Here's the most up to date list: warnings.ml

Probably unrelated to this list, but I also wanted to have a simple text field to fuzzy find particular warning numbers by description. In a similar manner how we did it with the Syntax Lookup Widget (using the Fuse.res bindings), but this can be done in another task.

[ryyppy]

Nice! One last thing:

Can we change the link within this section to point to the new warning-number list?

That will be the last change, otherwise it looks perfect!

[Minnozz]

We might want to link to the new warning list (or embed <WarningTable />) on some more pages: #190 (comment), most useful would be the syntax widget I think.

[ryyppy]

We might want to link to the new warning list

Yeah, in the attribute page we could add a link to the warning list in the description here:

You can find a full list of all available warnings [here](...)

most useful would be the syntax widget I think

I'd not include the whole table into different pages... should be enough to link to it, no? In the Syntax widget we use the See section to link to canonical resources

[Minnozz]

I've added some more links to and from the Warning Numbers page, and I also added the @@warning decorator to the syntax widget. I'm not entirely sure if I'm correct that it operates on the module level; somewhere else it is stated that it operates on the file.

[ryyppy]

this is looking sleek. Thanks!