Implement dtrt-indent-set

[ramnes]

Closes #82

[rrthomas]

Wow, this is great! Thanks for doing this.

What would you think about having a message if no variable can be found, when the function is called interactively? Would be nice to warn/explain to the user who might otherwise be confused when it has no effect.

[ramnes]

Why not, but then ideally we'd want to error before prompting the user for an offset, and I'm not sure how to do that. I'll eventually take a deeper look when I have some time to spare. :)

[rrthomas]

I think giving an error is the main thing, so while you're right, I don't think that matters, and I'd rather land the PR sooner; so, I'd be quite happy with just having a message output when there's no setting variable found and the function is called interactively.

[ramnes]

@rrthomas done then :)

[rrthomas]

Many thanks! New release shortly.