Hi, I want to customize output of markdown(`-f md`)/readme(`-f remark`?). But, current `--theme` options support only [html](https://github.com/documentationjs/documentation/blob/8ea9e834e5207b6071dc50a5877042af7cfd2a64/lib/output/html.js#L30) Is there any chance that support combination markdown/readme and theme option?