WIP draft ranges concept

[colinleach]

I split this out of the earlier Arrays draft.

The best exercise I can find for it is elixir/chessboard. We might want to expand that a bit, but it seems like a useful starting point.

Edit: Because go/chessboard is quite unlike the Elixir version, we could maybe take the most suitable features of each.

[colinleach]

I think this + the Chessboard exercise are now good to review. My local Git installation got corrupted somehow, so I hope I caught all the issues.

[colinleach]

The issues with config.json are getting silly. I've moved this back to draft. Once some of the earlier concepts are merged, I'll rebase onto main and have another attempt. At the moment, there are a lot of concept PRs open, and some of them are reusing old UUIDs - all very confusing.

I really wish we could have deleted all the old learning track stuff and started again from scratch, but Jeremy freaked when I suggested it. The link between GH and the Exercism website is complex and sometimes brittle, plus I used up all my credibility back in 2023 when I broke the R track with some over-enthusiastic changes (very embarrassing, and I'm keen to avoid a repeat).

[colinleach]

With so many earlier concepts now merged, adding this one to config.json is now easier. Not that that stopped me messing it up a couple of time!

[depial]

Only minor nits, which need not be addressed (however "an vector" should probably at least be made "a vector"