code: func lexLineComment(l *lexer) stateFn {
  	l.pos += Pos(len(lineComment))
  	for r := l.next(); !isEndOfLine(r) && r != eof; {
  		r = l.next()
  	}
  	l.backup()
  	l.emit(ItemComment)
  	return lexStatements
  }
docs: // lexLineComment scans a line comment. Left comment marker is known to be present.