[Developers] Website: example collection

[Hans Julius Skaug]

Hi All,

Examples (with admb files) are scattered around the website, and are not
very visible. This issue has been raised from time to time. 

What about creating an Examples tab at the top level (along with Documentation, Courses, etc)?
Second: agree on some kind of taxonomy of models. Third: maintain a list of
pointers to webpages where people put up their own models on their own webpages.

If we agree, and the tab is created, then I will take on moving/organizing all the random effects examples.

Hans