Feature: Add vertical offset to adjacent hints

[markstos]

This addresses #145 by adding some vertical offset when labels are next to each other,
clarifying that a child's label is not part of the parent's label.

I don't like that the offset is a fixed number here. I wanted it to be a percentage of the letter's
height. I tried this:

y = y+(i32::from(height) / 2) as i16;

But that was only right for a single overlap. For multiple-overlaps, the offset for the third
letter was doubled, so it was 100% lower than the one to the left instead of 50% lower.

This patch is also compatible with the most recent Sway branch, PR #138.

Screenshots

Before

After

[svenstaro]

Hey, sorry for not looking at this for all this time. I'm looking at this now!

[markstos]

Thanks.

[svenstaro]

Oh, I never submitted my review:

I like the idea but I wonder what the best way to go about this is. As it is, we already do have separation between the labels and at least in my configuration, they are quite distinct. Would you prefer a configurable vertical and horizontal multiplier perimeter? Perhaps slightly changing/alternating the tint or brightness of the labels would also be a good idea? What do you think?

[markstos]

In my patch, there's a fixed vertical offset. What I'd like ideally is a vertical offset is that gets small the deeper the nesting is. So perhaps the first offset is 40% of the height, the next 20%, the next 10%. There's rarely more nesting than that.

The problem with a consistent offset, say like 50%, is after two offsets one block is 100% below the other and looks bad. But if the initial offset is too small, like 10%, then it might look like bad alignment and not intentional.

I don't think a configurable horizontal offset is also necessary. Regarding colors, currently there's already colors for "focused" and "not focused", and I think adding more means of colors could confuse that. I've been using the simple vertical offset patch for about a year and it's been clear enough.

I didn't figure out how to make the offsets smaller with deeper nesting, though.