We noticed the rails gem increased in size between the beta and rc
versions, and the reason is that some guides images were updated but not
properly optimized, and one image changed from png to jpg, way bigger.

Converting the jpg image back to png, and using ImageOptim to optimize
all the images for web view, improves the situation [ci skip].

---

In current master/4-1-stable:

    508K  guides/assets/images/getting_started/

In v4.1.0.beta1:

    268K  guides/assets/images/getting_started/

In 4-0-stable

    328K  guides/assets/images/getting_started/

After the patch:

    260K  guides/assets/images/getting_started/

- Used Article model instead of Post as it may confuse with 'post'
  requests
- Tried to wrap the guide to 80 chars lines as much as possible.
- Removed unused image
- Fixes #13764

More to come.

I had written the original guide for "A Guide to Testing Rails
Applications". The current documents maintains the same structure and
examples I had drafted albeit with some minor changes to keep up with
newer version of Rails.

Older version which had credits included:
http://guides.rubyonrails.org/v2.3.11/testing.html

Github lifo/docrails History:
https://github.com/rails/rails/commits/ff359af86505b4d317b7467e7f79aa2ef2c5e795/railties/doc/guides/source/testing_rails_applications.txt

Used imageoptim, Saved few bytes
http://imageoptim.com/

Move 2 images to getting_started folder. All other images in getting started guide already in this folder.

When I updated these images, I must have gotten this one wrong. Now it's
right.

Fixes #9749.

Stuff didn't work because of strong_parameters. Now the right calls are
in place.

We changed the error style, so they're all wrong. Now they're right.
😄

The release notes is changed to include only the major changes and point
to the changelogs for the complete list. This lets us talk more about the
features included in the upcoming release and make the guide more useful
and interesting than just a list of all changelogs.

This is still a WIP guide pending a lot of work.

[ci skip]

plus:

* 80 column formats
* replacing the explanation of the dynamic_form gem with the example
  HTML/CSS that Rails scaffolds generate.

This reverts commit 33284014.

Reason: this change doesn't belong to DocRails.

Compressed all images from the guide through ImageOptim which saves sometimes up to 74.6% in size [ci skip]

Revert "Compressed all images from the guide through ImageOptim which saves sometimes up to 74.6% in size [ci skip]"

Reason: this change can't really be done in docrails,
see http://weblog.rubyonrails.org/2012/3/7/what-is-docrails/

This reverts commit bc06e8d7.

Compressed all images from the guide through ImageOptim which saves sometimes up to 74.6% in size [ci skip]

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