Added instructions for backporting changes to guides.

This reverts commit d77b576c.

Add Hash#deep_transform_keys and Hash#deep_transform_keys! Also convert ...

This option was added on cb6f8393
renaming the :wait_timeout option.

Fix build http://travis-ci.org/#!/rails/rails/jobs/1413405

Add Hash#deep_transform_keys and Hash#deep_transform_keys! Also convert deep_*_keys to use deep_transform_keys.

I was looking for instructions on backporting changes the other day and
wasn't able to find it anywhere. I updated the contrib guides based on
the disccusion in #6420, #6215 and #6447.

Add oscardelben to authors

Optimizing all images used in the guides

Add license field to gemspecs, by Matt Griffin

This reverts commit feaa7b35.

Reason: Incorrect change. That's a Rails 4 feature and will not
obviously work in 3.2.3.

[ci skip]

This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

ConnectionPool wait_timeout no longer used for different types of timeouts. #6441

Adding deep versions of stringify_keys and symbolize_keys (plain and bang) for nested hashes

An AR ConnectionSpec `wait_timeout` is pre-patch used for three
different things:

* mysql2 uses it for MySQL's own wait_timeout (how long MySQL
  should allow an idle connection before closing it), and
  defaults to 2592000 seconds.
* ConnectionPool uses it for "number of seconds to block and
  wait for a connection before giving up and raising a timeout error",
  default 5 seconds.
* ConnectionPool uses it for the Reaper, for deciding if a 'dead'
  connection can be reaped. Default 5 seconds.

Previously, if you want to change these from defaults, you need
to change them all together. This is problematic _especially_
for the mysql2/ConnectionPool conflict, you will generally _not_
want them to be the same, as evidenced by their wildly different
defaults. This has caused real problems for people #6441 #2894

But as long as we're changing this, forcing renaming the
ConnectionPool key to be more specific, it made sense
to seperate the two ConnectionPool uses too -- these two
types of ConnectionPool timeouts ought to be able to be
changed independently, you won't neccesarily want them
to be the same, even though the defaults are (currently)
the same.

Add Hash#transform_keys and Hash#transform_keys!

Change xml type datetime to dateTime

XmlMini define the xml 'datatime', but according to
http://www.w3.org/TR/xmlschema-2/#dateTime could be better
change this to 'dateTime' with upper case letter 'T.
So 'DateTime' and 'Time' are redefined from 'datetime' to 'dateTime'

add the changing to the changelog

Remove unnecessary comment.

Added session.keys and session.values back to ActionDispatch::Request::Session

Refactor date related input helpers

These tests check the values of 'min' and 'max' input attrs