Update docs

[joshkel]

Grammar and style: "TypeScript", add articles, etc.

Add docs covering the Array[] version of data. Please review and let me know if I've made any mistakes.

Fix an apparent mistake in the parsing: false description of category axes: I believe it's trying to say that strings would be a mistake.

[kurkle]

I'm not sure, but I'd suspect the common mistake of using integers for category scale was correct. When using strings, the scale automatically creates the labels array, but with integers it just tries to access the array at given indices.

[joshkel]

Thanks, @kurkle. Looking into this a little further:

I thought that this paragraph was specifically about use with parsing: false, but reading it again, it looks like I was mistaken.

From what I can tell in testing and from inspecting the source code, the category axis can take string labels or numeric indexes. Numeric indexes are its internal format.

Even if parsing: false is used, a plot that uses a category or time axis works if unparsed values are passed (e.g., if a category scale receives data like {x: 'January', y: 10 }). It looks like the data is assigned to meta._parsed, which seems to violate assumptions about how meta._parsed is used, but then scale methods like getPixelForValue check for unparsed data anyway, so it works. Based on the Chart.js docs, this seems accidental (or at least not guaranteed), so I assume it shouldn't be advertised.

I've updated this PR to try to be clearer. Let me know if this seems better.