Syntax Highlighting: Apply recent changes from DartCode.
Syntax Highlighting: Apply recent changes from DartCode.

- Remove obsolete "interface" keyword.
- Remove incorrect support.constant regex. (Dart-Code/Dart-Code#309)
- Recognize $ character in identifiers. (Dart-Code/Dart-Code#309)
- Highlight more characters within interpolated strings. (Dart-Code/Dart-Code#310)
dart-atom/dartlang,dart-atom/dartlang