NFData1,NFData2 instances (#767)

[dbeacham]

I've added NFData1 and NFData2 instances where appropriate for Data.Graph, Data.IntMap, Data.IntSet, Data.Map, Data.Sequence, Data.Set, Data.Tree and relevant internal dependencies

TODO:

• Check build across GHC versions
• Add @since docs

[meooow25]

This would be good to have. @dbeacham would you like to finish this PR?

[dbeacham]

Happy to - I'll finish it up next week.

[meooow25]

You could try the foldMap thing if you like, if not this looks good to me.

[meooow25]

Data.Graph could be misunderstood, SCC got the instance (not Graph). And IntSet is not affected.
We can also just drop the Data. and say "...for IntMap, Map, Set, Tree, SCC", I think that's good enough.

[treeowl]

Speaking of changes, we usually use @since TODO because we don't usually know what the actual next version number will be very far in advance. But if @meooow25 wants to make a release imminently, this could be fine.

[meooow25]

@dbeacham could you please correct the changelog so we can merge this? Also it needs a rebase.

[dbeacham]

That's done. I left the @since as it was but could update that as well if desired.

[meooow25]

There's a conflict preventing merge, please rebase on latest master.