Move the docs for constructors and operators out of methods section

[aaronfranke]

I'm interested in improving the documentation for operators, but before I do, I think it would be a significant improvement to separate operators from regular methods. We may as well do this with constructors too. Constructors and operators are very different from regular methods, so it makes sense that they should be separate.

I'm not very familiar with this code. This PR has not been thoroughly tested, there's likely things missing, and it's likely that the code can be simplified to not have so much duplication (would involve a fair amount of refactoring though). I assume there will also need to be updates for the docs repo so that it can read these new sections (I haven't touched the Python scripts). If anyone more knowledgeable can fix any remaining issues with this, feel free to use this PR as a base.

Anyway, the basics do work. Here is an example of how Color shows up in the editor. Previously everything was all together in one "Methods" section. Now constructors and operators get their own categories.

The descriptions work too, here's the "Operator Descriptions" section (they do work, but these ones have no description).

Here's what it looks like in the XML files, there are now sections for constructors and operators:

[mhilbrunner]

Seems like a good improvement to me.
If we do this, we should do the same for the online docs.

[YuriSizov]

If we do this, we should do the same for the online docs.

In fact, I think after this PR syncing will remove all those moved items from the online docs. But I think it's okay to update makerst.py in a separate PR. Should be pretty trivial.

[akien-mga]

Needs rebase.

[akien-mga]

Thanks!