go-counting: Rewrite tests to use hspec with fail-fast.

[rbasso]

• Completely rewrite tests to use hspec.
• Add test suite's dependency on package multiset.

Related to #211.

This was one of the most challenging re-writings since we started migrating the exercises to hspec, so I think I owe a few explanations:

• shouldScore is pointfree madness, but I couldn't make it more readable any other way.
• toOccurList . fromOccurList is the best way I could find to sum all the scores.
• first and swap are not commonly used in this repository, but I think they really make sense.

[petertseng]

shouldScore is pointfree madness, but I couldn't make it more readable any other way.

It didn't seem so hard to understand to me. It gets harder for me if I see compositions of compositions, like

 > pl \x y z -> f (g x y z)
 ((f .) .) . g

toOccurList . fromOccurList is the best way I could find to sum all the scores.

That seems OK. Shorter than what I might have come up with (which would be folding with insertWithKey then toList

[petertseng]

These new tests seem easier to read, so I like how shouldHaveTerritories and shouldScore were done!

[petertseng]

(OK I realize shouldHaveTerritories is pretty much the same as terrs helper of the previous, but shouldScore I think has improved compared to the original because it makes clear which score belongs to whom)

[rbasso]

Thank you very much, @petertseng! 😄