[OSBEv4] HTML Themes as Org Links!

People have reached out about the themes I use, so I thought I'd make it a breeze to export Org files with any theme: The image is me pressing `C-c C-e h o` twice, but not changing the underlying Org source ---of-course you can select your themes from a completing read menu, as show in the image's tooltip. This, among other things, is part of the v4 release of [org-special-block-extras](https://github.com/alhassy/org-special-block-extras) \---sadly I haven't yet gotten around to making a proper changelog or updating existing docs.