'make book': Create a book version of Snabb Switch code.

Create snabbswitch.pdf (and .html and .epub) by very lightly
converting the sources to Markdown and then running them through
pandoc.

See doc/genbook.sh for the main glue.
intel.lua: Converted to ASCII.

Removed some Unicode characters that had come in via copy & paste from
the data sheet.
Superficial layout changes.

To make sources pretty-print in book format better.