build diagnostics for referencial integrity

[vroland]

When implementing better handling for internal references, I noticed many internal links are not valid any more. Many of those are referring to old anchors.

[kulla]

Is there an HTML page showing those malfunctioning links or can we create such a statistic?

[vroland]

https://mathe-builds.serlo.org/nightly/Benutzer%40COLON%40Valentin_Roland%40SLASH%40Analysis_1/861124/stats/verbose/861124.stats.html

See unresolved references. I still have to test wether self-references ([[#anker:bla]]) do work, but actually I'd like to deprecate them, too in favor of full references ([[Mfnf: ...#anker:bla]]).

[kulla]

I have fixed the remaining mailfunctioned references.

[vroland]

nice!