* Accessibility Sans Serif Option
This adds another build processs where the book is built using a sans
serif font. This can facilitate reading the book for some users.
* Update readme
This adds a `make export_figures` command which exports all the flow
charts into nicely looking pngs. The command requires that you have
docker running locally.
the makefile has three targets
* all, which does the complete build
* fast, which only runs pdflatex once
* clean, that removes files generated by the makefile