Remove all highlight tags from the documentation

Use Markdown's fenced code blocks instead of Jekyll's Liquid tag for
syntax highlighting.
Fix various typos and deprecated code in guides

Update the typos in most guides and also update or remove some
deprecated code. The following documents have been updated:
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)
Update informative files

Update files for contributors and/or readers such as the index file
and the contribution file
Remove the "ga.html" include