* Fix issue of book not building
* add dependencies
* fix
* test make4ht
* fix cmd
* Use own docker image
* Add label
* fix urls
* Add validate command
* build non mac version
* tmp run
* use smaller tex version
* build full
The README says `make release` should build the ebooks, but it's
building the PDF (same command as in `make build_book`). Maybe this
should run `make release` inside the books folder?