Link to a complete source from doc popups

The doc window in autocomplete and doc-on-hover has the first part of the documentation for a symbol, but it's often cut off. Ideally, it would contain a link to the full documentation. For built-in symbols, this link could open the guide to the generated haddock for the symbol (this requires understanding haddock's anchor format...). For symbols defined in the code, it could act like a go-to-definition feature.

(For doc-on-hover, this implies making a change so that it's possible to click on the doc window at all. The obvious candidate here is to make the doc location "stickier", so that once it opens, it remains in the same place even when the mouse moves, so long as the mouse is over the same symbol, or is hovering over the doc window.)