Tomorrow themes: improve HTML and XML highlighting

[itiut]

This adds some improvements for HTML and XML highlighting and minor changes for CSS highlighting.

First, this fixes HTML and XML highlighting where all the tags became red, and introduces new highlighting colors referring to Base16 Tomorrow theme:

• symbols (<, >, /, =): default foreground color
• id attribute: blue
• other attributes: orange

And, this adds some changes in CSS highlighting colors:

• ID selectors: red -> blue
• class selectors: red -> orange
  • These two are the result of the new HTML attribute colors.
• element selectors: purple -> red
  • It's intended to make consistent with the red color of HTML tag names.

Screenshots of Tomorrow Night

Before

After

[noinkling]

Just to chip in: Interestingly if you go to http://colorsublime.com/?q=tomorrow, click on "Preview" for Tomorrow Night (or any of the Tomorrow family), and click on HTML, you can see it also looks quite different to the wall of red you get in VS Code, presumably due to differences in syntax definition/grammar.

Additionally, in Sublime it looks like this:

which still isn't great, but better than VS Code.

For some extra perspective, Atom comes with the Base16 version of Tomorrow (light & dark), which @itiut linked above. You can already get this in VS Code through the "Base16 Themes" extension, which would be great, however there are notable differences to how it appears in Atom, for example white quotes around attribute values in HTML. Or using a snippet of JS as an example...

VS Code:

(notice white quotes)

Atom:

The standard Tomorrow Night in VS Code is slightly different again from both these examples - in my opinion slightly nicer - which is why I'm +1 on this PR, because to me that's kinda the best of both worlds (though still far from perfect, e.g. interpolated strings). But it also means effectively creating a fork of the themes, and maybe some of this stuff could better be fixed by improving the syntax definitions or attempting to contribute changes upstream.

But whatever happens, the standard Tomorrow themes really aren't suitable for editing HTML in VS Code as they stand, which is really unfortunate, a sentiment echoed in the reviews on the marketplace.

[aeschli]

We might want to wait to see how the latest vscode-textmate fixes impact the rendering of this theme. Instead of matching the theme scopes to a flattened list of grammar scopes, we then correctly match against the scope hierarchy. This will fix many outstanding issues of coloring differences between vscode and other editors.