Improvement: provide an .epub version of the book with releases

**Is your feature request related to a problem? Please describe.** No problem, just a suggestion. **Describe the solution you'd like** It would be great to have a .epub version in addition to the .pdf version to better read the book on ereaders. .pdf files don't reflowable nor resize well which makes them that much harder to read. **Describe alternatives you've considered** - **Additional context** vscode-pandoc could be used to do it in one click from the .md files (similar to creating the .pdf) in VSCodium.