Navigation links fixes

Here are Eng + Rus epub book versions with navigation fixed.
I hope the problems with failed opening on some ebook readers are done, but we still want to get feedback from users.
Known issue :

• external links are not opened (wip)

0.0.1-alpha epub book version

An draft book version for English and Russian.

That's not a 'No Starch Press' book. Books are generated from TRPL MD sources. English and Russian versions are present.

There are following known problems with that now:

• some ebook readers fail opening it (known problem, work in progress)
• external links are not opened (known problem)