Add Dhall support

[sphw]

This PR adds Dhall support using serde_dhall, a native Rust implementation of Dhall. Dhall is a functional configuration language designed to make composition of configuration files easier.

closes #123

[matthiasbeyer]

Hi,

Awesome, thanks for your contribution!

In general this looks good. The TODO item could be fixed right away, right?

Also (I tested this because I was not 100% sure whether it would work), the from_dhall_value() function does not need to clone.

Here is a patch for that: matthiasbeyer@7a163a7
And here's another patch you could apply: matthiasbeyer@91dafd1

I guess you can just git pull --ff-only https://github.com/matthiasbeyer/config-rs/ pr-218 if you want to apply these 😄

[matthiasbeyer]

Plus, I messed up the formatting (thank god we have CI for that), here's the patch that fixes it: matthiasbeyer@00ed90b

You can of course still use the git pull --ff-only line from above, the patch was pushed to this branch and a git rebase --autosquash -i master will squash the fixup away 😄

Sorry for messing this up...

[sphw]

@matthiasbeyer Thanks for the timely and thorough review

I integrated all your requested changes and comments, and then squashed them into a single commit. I also fixed the error handling case you mentioned above.

Let me know if you have any other comments

[matthiasbeyer]

Looks good.

No need to squash things into one commit, though. That only makes reviewing harder. For the next time, then... 😆

[MGlolenstine]

I have published a PR that should fix the problems during the build.
All tests should succeed now.

[polarathene]

@matthiasbeyer it looks like this PR is going stale too? The build PR referenced last in Dec 2021 was merged, and no remaining concerns with this PR for being merged?

[matthiasbeyer]

Yep so there's conflicts and this PR needs rebasing.

[polarathene]

Yep so there's conflicts and this PR needs rebasing.

Done: #466

@sphw can update their branch here, otherwise my alternative one should be sufficient if they're unresponsive.

[sphw]

@polarathene I'm closing in favor of your PR, since this has been sitting for almost 2 years now lol. Thanks so much for helping to push it over the finish line.