should doc-kit re-introduce prev / next buttons (CrossLink)

[bmuenzenmeyer]

https://nodejs.org/learn for example regressed when we converted to doc-kit

[AugustinMauroy]

for learn yes for api docs

[bmuenzenmeyer]

agree we should start with supported it in doc-kit, and then perhaps only turn on in learn

[avivkeller]

How would we define what is "Next" and what is "Prev". I would imagine this would be involve a change of our SideBar to import a user-supplied (or generated, if omitted) #theme/navigation or something, which is used to both populate the side bar and determine the CrossLinks