Proposals better jsx mark up + some minor changes

[RaulCote]

Hello,

I enjoy this colorscheme and plugin. Congrats for the work, really appreciate it. I open this PR to propose some small changes. Everything is explained on the commit messages but mostly I noticed the selected yellow was darker than the one used on the original onedark palette, this makes that the difference between orange / yellow was hard to see. Visual Studio Code dark them uses orange for HTML / React component attributes and yellow for the component name. This trick is pretty nice if you put italic for the attribute as well. That's the biggest change this PR propose. Find below the complete list.

Total Changes:

• Buffer separations set to dark instead of white. More minimal.
• Changed yellow color to same as original onedark.
• Cursor Line set to dark, blue was difficult to see.
• Folding also set to dark, looks more in place.
• TSVariables set to yellow. On this small file it doesn't make much difference but on big files full of variables everything was almost red, which doesn't look that great. Better yellow as the predominant color.
• Booleans as orange. Same as in Visual Studio Code.
• Html / React attributes as orange and italic if chosen.. same as in Visual Studio Code.

Now:

Before:

Feel free to apply changes to the PR if you don't like something. As said, these are proposals.

[monsonjeremy]

Thanks for doing this, looks great!