Use fenced code blocks instead of highlight tags

Rely on Markdown's fenced code blocks instead of Jekyll Liquid tag
Update informative files

Update files for contributors and/or readers such as the index file
and the contribution file
Update the configuration for fenced code blocks

The fenced code block syntax is provided by Redcarpet so the Jekyll's
configuration should be updated to make them work and also ensure the
site looks the same at some levels (e.g.: tables)
Fix various typos and deprecated code in guides

Update the typos in most guides and also update or remove some
deprecated code.
Merge pull request #316 from robin850/master

Documentation update