Fix missing types in signatures

[tingerrr]

Resolves #9 by adding a missing else branch for types that have no Typst documentation links.

I'm not sure if this is actually correct, it seemed that some types were missing even when they had a Typst docs link, so the type map was not complete.

[tingerrr]

I've added content too, for now I haven't found a page or auto or none, this is consistent with the docs' website which doesn't link to those, but the other types.

[tingerrr]

I have gone ahead and also fixed the highlighting for str by renaming string to str and adding a type mapping from string to str. Since the docs refer str not string.

[jneug]

Thanks. Looks good.