Automatic compilation of Pro Git 2 Chinese to PDF and epub

The compilation uses asciidoctor to generate the ebooks and the PDF. That needed to reorganize the files to fit with the requirements of the tools.
See https://github.com/progit/progit2-zh/commit/315678522c4a85f0e716931511b1cb369eb74f05

One additional difficulty was that Chinese is part of CJK languages for which the layout of PDF needs to be adapted in asciidoctor by using the tools provided by @chloerei

The compilation is automatically run on Travis- CI
at https://travis-ci.org/progit/progit2-zh
. The ebook is checked for internal consistency with epubcheck and the corresponding revision is tagged if everything is ok.

This build is orchestrated by pulling files from another dedicated repository https://progit/progit2-pub

Then the files are uploaded to the release and made available in github, but also on
https://git-scm.com/book/zh

This is part of the general effort to produce ebooks for all translations of Pro Git. I hope in the near future to be able to run for Japanese, Korean , Indonesian and many more.