Add bracket highlight for atom, esp on the same line

[emilong]

Hi!

I was having trouble seeing matching brackets, especially on the same line, so I thought I'd try to highlight them. I just picked a high-visibility color in the theme and am happy to change that choice, but the hard part here (for me) was figuring out the way atom does its layering in these cases. It puts the highlight below the current cursor line, so I popped it up with the z-index, but you can't see the underlying character without setting an alpha.

Current:

With this change:

Even if this doesn't go in, I'd love to see some bracket matching in the theme. 😄

Thanks!

[Vectornaut]

Here's another possibility for the highlight style, which I chose while porting the theme to GtkSourceView. It colors the matched bracket strawberry (#FF857F). It works okay even in languages where brackets are colored pink. I don't think brackets are likely to be colored strawberry. They'd have to be classified as function argument for that to happen.

For me, only coloring the text gives a good balance between visibility and distraction. The highlighting stands out more when the cursor is in motion, because the color change calls attention.