Bump newrelic gem to version 3.5.3.25.
Update the list of available languages for the book.

The algorithm applied is quite simple:

1. Run `summary.rb` in the progit working dir
2. Languages with 99% or above are fully translated
3. Languages with 10% or above are partially translated
Merge pull request #225 from jnavila/update_book-langs

Update the list of available languages for the book.
Merge master into bump-newrelic-gem-version.
[book] Update procedure to generate book
Merge pull request #217 from github/bump-newrelic-gem-version

Bump newrelic gem to version 3.5.3.25.
Merge pull request #230 from jnavila/update_book_doc

[book] Update procedure to generate book
[book] tidy chapter when regenerating it

 * Remove a chapter if it contains no sections
 * Remove sections which are not present in the chapter
Add Ry's Git Tutorial to External Links page
Updated Rails to 3.2.11
add new Packt Publishing git book

This is a new git book coming out in January 2013. I haven't
seen it yet, so I don't know about the quality, but I think
we are better to be inclusive in this list. There are not
that many git books, and unless one of them is known to be
really terrible or obsolete, I don't see any reason not to
link to them all.
Merge pull request #234 from ryanhodson/rys-git-tutorial

Add Ry's Git Tutorial to External Links page
Merge pull request #236 from andrew/rails-upgrade

Updated Rails to 3.2.11
Merge pull request #237 from github/packt-publishing-book

add new Packt Publishing git book
Use chapter title when section title is blank
Merge pull request #238 from github/chapter-page-title

Use chapter title when section title is blank
Merge pull request #231 from jnavila/book_tidy_chapters

[book] tidy chapter when regenerating it
Typo.
Merge pull request #246 from 75lb/master

Typo
fixed placement of book icon