[Makefile] [doc/genbook.sh] Simplify `genbook.sh' and make `make
doc/snabbswitch.md` work again.
[genbook] Include version in metadata and only include authors
with full name (at least first+last name).
[make book] Remove epub task for now, make html task produce
self contained file which uses doc/style.css .
[documentation] Repair pdf and epub targets.
[scripts/process-markdown] Center diagrams.
[doc/style.css] Center figures.
[documentation] Merry Christmas Snabb Switch! :) (Huge documentation
commit)