Publish eBook in epub and mobi formats

Would be cool if we can build this book in epub and mobi(for Kindle) format, some interesting ideas are:

- [ ] Setup an make file for building the epub version with `pandoc`
- [ ] A really cool stylesheet for great typesetting in epub
- a great base for this is the [Standard Ebooks](https://standardebooks.org/) stylesheet
- i've modified already the style for the [Category Theory for Programmers](https://github.com/onlurking/category-theory-for-programmers), but is in need of improvements, both projects can benefit
- [ ] Setup the conversion from epub to mobi using [kindlegen](https://www.amazon.com/gp/feature.html?docId=1000765211) in the makefile
- [ ] Setup `Travis CI` or `CircleCI` within the repository for automatic build
- also fail building when dead links are found