message: Implement mixin token
diff: @@ -504,6 +504,24 @@ export const plugin: Plugin = {
  result += `+${token.val}(${token.args})`;
  break;
  case 'mixin':
  + if (previousToken) {
  + switch (previousToken.type) {
  + case 'newline':
  + case 'outdent':
  + result += indent.repeat(indentLevel);
  + break;
  + case 'indent':
  + result += indent;
  + break;
  + }
  + }
  + result += `mixin ${token.val}`;
  + let mixinArgs: string | null = token.args;
  + if (mixinArgs) {
  + mixinArgs = mixinArgs.trim();
  + mixinArgs = mixinArgs.replace(/\s\s+/g, ' ');
  + result += `(${mixinArgs})`;
  + }
  break;
  case 'if':
  break;
  