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.
Better localized language name for Chinese.
Add a new top-level section (with underscores, _)

user-manual.txt underlines the page title with underscores (_):

  Git User's Manual (for version 1.5.3 or newer)
  ______________________________________________

The major sections are underlined with equals signs (=).  This is
causing the page to be truncated before the second major section
(Exploring Git history) [1].

With this commit, we should get the whole manual, but it might also
cause problems by demoting all other section headers (<h1> -> <h2>).
It *shouldn't* cause problems, since HTML5 only uses relative header
sizes for implicit sectioning [2], but that doesn't mean it won't ;).

[1]: http://git-scm.com/docs/user-manual.html
[2]: http://www.w3.org/html/wg/drafts/html/master/sections.html#headings-and-sections
Merge pull request #280 from wking/user-manual-truncation

user-manual.html truncated after the first section
Merge pull request #272 from jnavila/add_tables_to_progit

Add table processing  to the Progit book
Merge branch 'master' of https://github.com/github/gitscm-next into rails4
Merge branch 'master' of git://github.com/adamme/gitscm-next into adamme-master
Merge branch 'master' of https://github.com/github/gitscm-next into rails4
Update app to rails 4.0
Use RSpec
generated by Rails upgrade
Update book spec