Supports various table outputs

*as discussed with @higgi13425 today*
- [ ] docx (@higgi13425 recommends considering [`flextable`](https://davidgohel.github.io/flextable/))
- [x] html with [`kableExtra`](http://haozhu233.github.io/kableExtra/awesome_table_in_html.html)
- [ ] LaTeX-pdf with [`kableExtra`](http://haozhu233.github.io/kableExtra/awesome_table_in_pdf.pdf)

