Add tables capability to the markdown parser

This is to prepare the migration of the progit sources to real tables
made in PHP markdown.
Include evolution of the generation script in the rebuild test

This changeset modifies the hash code saved in db for the skip test
to include the tracking of the script itself. That means that all
the pages of the book are regenerated whenever the script changes.
Process tables in the book

Preprocess the markdown files to change the tables into a format which
RedCarpet can convert to a HTML table. Then add a class to this table so
that we can apply css on it.
Merge pull request #272 from jnavila/add_tables_to_progit

Add table processing  to the Progit book