The PVP should include advice about SafeHaskell

[andreasabel]

The PVP does at the moment not give any advice about SafeHaskell. E.g. it does not say that if you make a previously Safe module unsafe, then you need a major version bump.
Why major bump? Because then import safe statements suddenly error out, and downstream packages become unbuildable.

In the wild:

• https://github.com/haskell/directory/issues/147

In directory-1.3.8.0, the module System.Directory is no longer Safe, as it used to be in 1.3.7.*. Thus the new release should rather have been directory-1.4.0.0. Being released as 1.3.8.0, packages using directory < 1.4 and import safe System.Directory are now broken and need a revision.

[phadej]

Is this duplicate of #22

[phadej]

Closing as duplicate of #22