History: Updating a Tiki theme from Bootstrap 3 to 4

This document is a work in progress, as Bootstrap 4 is still in beta at the time of this writing. But theme-related details are probably pretty stable so the method described here should continue to be useful.

The Bootstrap developers have taken pains to facilitate custom themes compared to what was offered for release 3, and this helps us as Tiki theme creators/maintainers. For an overview of (generic) Bootstrap theming, see http://getbootstrap.com/docs/4.0/getting-started/theming/.

(Description coming soon.)