minor fixes and enhancements

closes #2
1. fix (remove) highlighting for `Blade's ignore markers` when `@` used
2. make `comment block` backcolor alittle bit darker
3. add highlight for `punctuation.definition.expression` (braces of $variable inside double-quoted string)
4. add mention to `Laravel-Blade-Highlighter` package
5. add `Embedded Code` to the `Enhancement` list