Deprecating functions

[Herbert Valerio Riedel]

On 2015-01-09 at 11:18:02 +0100, Jan Stolarek wrote:

> The reall 
> question is how to remember that we should remove this at some point?

This affects all exposed libraries; I think it's enough to simply make
this part of the release-procedure at some point in the release-cycle,
to actively scan all DEPRECATIONs, and decide for each whether to kill
them or let them live for another cycle.

It simplifies things though, if it's obvious when a deprecation was
declared so one doesn't have to `git blame` for it. Many deprecations
already have a comment attached like "deprecated in GHC x.y"