Vision document for H1 2017

[Sönke Ludwig via Digitalmars-d-announce]

> - tagging instead of hierarchical categories

The categories are in fact just a form of hierarchical tags. This is 
quite useful, because applying a tag will bring in the ancestor tags for 
free. The UI for both, applying tags and filtering, could be better, 
though. And some form of crowd sourced management of available tags 
could also be interesting to think about.