Switch to reStructuredText + sphinx

[multun]

This pull request does the following:

• convert the book from org-mode to reStructuredText
• switch from emacs-org-mode to sphinx
• add support for i18n with collaborative translation
• split the book to get one file per chapter
• update the CI to build ebooks + a website version in addition to the pdf, both in French and English (the French version has no translated strings yet)

Moving to rst + sphinx has a number of avantages:

• ease of translation: sphinx can generate .pot files, which can be exported into a number of collaborative translation tools. I did setup a transifex organisation, but pretty much any other tool would work. Adding a language is as easy as pulling in new translation files, and adding the language to the build script. Any update to the source file can be pushed into the translation tool, people can translate the new strings, which can then be pulled into the repository.
• rst has a far better editor support than org-mode
• sphinx can convert rst to many file formats, including html, latex and epub

As this pull request touches every single line of source in the repository, it probably broke something. It really needs some testing.

You can preview an html build at https://crypto101.multun.net/

I also intend to help translate the book into french.

Known issues:

• with latex, bibliography entries don't have backlinks to their references, due to a bug of pagebackref
• the single page html build has incorrect links due to sphinx not handling merging multiple documents into one properly
• the margins aren't the same as the org-mode version
• the advanced warnings could look better
• add subfigures support to sphinx and ditch the static matrix-illustration.tex (needed to translate subfigure captions)
• a translation guide is still missing
• references to the glossary are gone, they must be added back using :term:

Thanks @lvh for your amazing book! Do you want the ownership of the crypto101 transifex organisation?

Fixes #62
Related to #362 #348

[multun]

@lvh I think it's ready!

[lvh]

@multun Hey, just a heads up with a little luck I'll be reviewing this today. Thanks again for all the work you've put in here.

[lvh]

@multun I think ownership of the Transifex organization makes sense.

[multun]

@lvh cool! send me your username, and I'll do just that

[lvh]

Bizarrely, lvh was taken but ostensibly not by me; https://www.transifex.com/user/profile/lvh_/ is me though :)

[lvh]

@multun Do you have any examples of this issue:

• the single page html build has incorrect links due to sphinx not handling merging multiple documents into one properly

The links I found appeared to mostly work?

[multun]

It only occurs with auto-numbered footnotes ([#]) / figures, all links with a name work fine
@lvh your profile is private, I can't invite you :(

[lvh]

@multun oops, sorry, try again :)

[multun]

@lvh you now are administrator and maintainer of the crypto101 organization! It's pretty empty for now, but I'm pretty sure it'll change soon :)

[lvh]

Thanks!

I've been hitting a snag with the build via docker:

Writing index file crypto101.idx 
! Undefined control sequence.
\csq@main@language ->\xpg@main@language 
                                        
l.124 \begin{document}

I'll try and figure out what's up with that. I imagine it's a dirty build dir.

[lvh]

I think what might have happened is that I was using the wrong language code. I used en_US instead of en. Could we add the style of language code to the README please? Are other styles of codes allowed? Could I stuff $LANG in there and expect it to work?

[multun]

Here's the list, I'll update the readme soon
Unfortunately sphinx's language codes aren't like LANG's

[multun]

@lvh I added some documentation about language codes, sorry for the delay

[lvh]

There should probably be a ticket for caching the docker build, since right now it downloads a lot of stuff every time.

[multun]

I pushed a built image to the docker hub, you can get it with docker pull multun/crypto101:1.0
Once you either built the image once or got it from the hub, it shouldn't be needed to rebuild anything ever.

[lvh]

This is enough of an improvement (and has been open long enough) that I'm just going to merge it, and we'll deal with any remaining issues as they come.

Thanks @multun!!!