Ambiguous link guidance

[j-mie6]

When working with Scaladoc, it can be annoying to work out the correct way of dealing with ambiguous links.

This PR adds a section to the "Scaladoc for Library Authors" page to address this, clearing up exactly how this should be done. There appear to be a couple of bugs/holes in the disambiguator, so I've added them there as cautionary tales too.

(Compiler should now point at this page instead of its own quick guide, implemented in scala/scala#10458, pending this merging).

[som-snytt]

Tweaks and typos. Lots of good information.

If I select "request changes", then I'm on the hook to re-review?

It's already very useful info. The text can be amended later, if desired. Or now, if possible.

[SethTisue]

@julienrf does the Center have a Scaladoc expert who would like to take a look? (if not, let's just hit merge?)

[som-snytt]

Scala Center's charter should mandate that it have a Scaladoc expert on call 24/7. A Scaladoc doc.

@j-mie6 for future reference, if you at-notify someone in a commit message, they receive spam on every rebase. If your typo was intentional, thanks for that!

I will use that clever hack, @SethTissue! Maybe we can elicit further input from @oderski.

[j-mie6]

Let's say that the typo was intentional. Didn't actually realise that a tag in a commit actually... Well... Tagged.

[som-snytt]

In case I misremembered or github notifications have changed, I will alert you on my next PR and we will learn the truth. Certainly, mentioning a ticket will spam the comments on the issue. Also, if I remember to try that experiment, "Apologies in Advance"!

[j-mie6]

Why is there no 😱 react GitHub...

[julienrf]

@j-mie6 Thank you!