Ribbons are just R scripts.
Update for ipynb format.

See also tinsel commit 289b088db7a8a5832553d469db2ecf2264eeb4ce.
Fix some whitespace issues.
Switch rendering to rmarkdown::render.
Add html output download link.
Add source download link.
Whitespace cleanup.
Factor out tinsel code.
Disable sidebar.
Use fixedPage instead of fluidPage.