Unreadable: Highlight symbol and highlight thing (Fix Provided!)

[ianyepan]

Highlight-symbol and highlight-thing are two similar packages that provide the ability to highlight all identical symbol at current cursor point. It is a widely adopted feature in most of the modern editors, e.g. Visual Studio Code, IntelliJ IDEA, Sublime Text, Atom, CLion etc.

Currently, Zenburn has no support for its background face, so it defaults to #4d4d4d, which is IME too close to the Zenburn background colour, making it too hard to read. Therefore, I suggest we change it to a brighter #5f5f5f.

Here's a quick before-and-after:

Current appearance (notice that root is 'barely' highlighted)

My proposal

And here's a reference of how highlight-symbol looks like in other modern editors; Example: Visual Studio Code:

In the meanwhile, I'll work on a pull request to fix this.

[ianyepan]

PR submitted, waiting for review