add support for # title {.tabset}

[Leo-Lee15]

Thanks for this awesome package!

I've found the # title {.tabset} feature in plain rmarkdown very useful (see the following screenshot for example). But it seems this feature is not supported in prettydoc package.

Would you mind considering adding this feature into the prettydoc package.? Thanks!

[yixuan]

The difficulty is that tabset heavily depends on the Bootstrap library, which prettydoc intentionally tries to avoid. Perhaps there are other nice rmarkdown templates that are based on Bootstrap and have this feature built in.

[Leo-Lee15]

Thanks!