Build contributors.txt once again

Asciidoctor (happi#66)

* Use asciidoctor to generate HTML version of the book
* Fix a few diagrams
* Style images
* Additions to .gitignore file
* Minor fixes

Moving chapter files to chapters dir. (happi#33)

* Moving chapter files to chapters dir.

* Adding .gitignore to make sure we have an ebin.

* Add .gitignore to make keep xml dir.

* Fix shell language.

* Remove revision history and add git contributers.

* Fix build.

* Fixing contributors generator.