Add count link to avoid duplicates URL about doc-linter-rules

[MatonAnthony]

Comment from @a2sheppy in mdn/doc-linter-webextension#15 :

Ideally we would get the following information:

A warning if there are more than 100 links total within the body (including those generated by macros, preferably)
An error if there are more than 250 links total within the body
Warnings if there are more than some given number of links to the same page (I'm not sure right now what that number is)

[MatonAnthony]

Most macros are having constant numbers of links generated, so we could do a list with the numbers inside the macros.

(All the macros with XRef in their names would be a good start and also HTMLElements, HTTPHeaders, Bug)

[MatonAnthony]

Considering that we listed the numbers of link for each whitelisted / non-deprecated macros and that most of them only represents one link.

It doesn't seem pertinent to maintain a matching list macros -> number of links.
Especially considering that the linting-rules are only giving informations and not enforcing anything.

[MatonAnthony]

Test implemented in #8