Build example book

[davidandrewthompson]

bookshop should come with an example of a proof-of-concept book that can be build from the markdown source into HTML.

The book should be built around https://alistapart.com/article/boom/ so that we can add a print-pdf via

• PrinceXML
• or wkhtmltopdf (open source but lacking as many features)

[worlduniting]

This should only be for HTML.

PrinceXML and pdf conversion should be a separate issue.