Update song exercises

[ErikSchierboom]

There are multiple song-related exercises:

• house
• beer-song
• twelve-days
• proverb
• food-chain

These exercise have all been updated to have a similar structure. This includes having the return value be an array of strings, instead of a big string. We should decide if we want to follow that approach or still use strings. What do you think?

[robkeim]

I'm usually a fan of following the canonical data (where it makes sense), but I didn't read the entire thread on why they changed to the array format to represent these instead of a single string. @ErikSchierboom do you know?

My gut feel would be that having a string seems more natural but I don't have a strong enough argument for that to convince myself it's worth straying away from the canonical data. I could definitely be convinced that's the right direction to go in though :)

[ErikSchierboom]

I don't recall exactly why the array approach was chosen. I'm not really for or against an approach, although in the F# track I've used lists for the expected result, not strings.

[robkeim]

In that case I'd say let's go with the path of least resistance :)

From a student perspective I think the array approach might be slightly more difficult, but nothing considerable. How about in terms of maintenance for us?

[ErikSchierboom]

I don't think it matters much :)

[ErikSchierboom]

I'm working on this