Remove Groovy-based EPUB generation script
The `epub:generate` Rake task has been inspired by `make_epub.sh`.
Unfortunately, `make_epub.sh` requires Groovy to be installed and
unconditionally rebuilds all the intermediate files when a single file
has been changed.
Added ProGit.css for better list layout and better code formatting, m…
…ake_epub.sh cleaned up
Add script to create epub