Remove N0 and D.V.F.Cont.mk0

They are synonyms to Z and empty respectively
Bump version
Added tag v0.5.1.0 for changeset e112a00c905f
Move changelog to separate file
Update changelog
Bump version
Add ChangeLog to list of files and use correct haddock markup

(It's not rendered correctly on site for some reason. Locally everything
is OK
Bump
Added tag v0.5.1.2 for changeset 2f3de94874ab
Add documentation about problems with tuples
Use cons