Syntax highlighting keywords

[keertip]

Editor feedback:

When using the words "source", "import", or "library" as identifiers in a program, they are highlighted as keywords. When writing a lexer, for example, this getrs really confusing when you have a class with a "source" property (or getter).

class Lexer {
 Source _source;
 Lexer(this._source);

 // "source()" is highlighted as a keyword, but in this content it shouldn't be.
 Source get source() => _source;

 // �
}

[stevemessick]

Added Fixed label.