Merge pull request #12009 from wangjohn/fixtures_fix

Removing instances of string class_names in fixtures.
Merge pull request #12014 from wangjohn/change_deprecation_horizon

Changing deprecation_horizon to be Rails 4.2
Make AV dependency for ActionMailer
PG adapter deals with negative money values formatted with parenthesis.

Closes #11899.
Merge pull request #11396 from strzalek/extract_renderers

Remove dependency on Action View from Action Pack

This set of changes removes the need of using Action View with Action Pack.
Now you may use controllers without Action View, by rendering `:text` response
or alternatively you can plug in your own rendering logic. This is especially
handy when you're just dealing with APIs and don't need to include entire
Action View just to render simple JSON responses.
Merge pull request #11973 from prathamesh-sonpatki/nokogiri-warning

Add error message for including nokogiri in Gemfile for rake doc:guides
Merge pull request #11827 from vipulnsward/remove_extra_case

Remove extra case.
Merge pull request #11997 from startupjockey/add_credits_AS

Adds Akshay Surve to Rails Guides credits list [ci skip]
fix typo in the credit section of the guides. [ci skip]
Add Finder API changes to upgrading guide [skip ci]
Warning on doc for assets under lib|vendor not precompiling
Merge pull request #12015 from vipulnsward/add_dynamic_finders_to_upgrade

Add Finder API changes to upgrading guide [ci skip]
Soften wording about knowing other devs.

Many people don't, so point them to a place where they can meet
some.
Flesh out feedback portion of contributing guide.

I don't know of anyone that hangs out in #rails-contrib, and we should
also let people know that feedback can take some time.
Add note about features vs. bugs.

Sometimes people ask what makes a feature and what makes a bug, so
let's clarify that so we can show it to people later.
Updating README.md [ci skip]

Updating the global Rails README following work by @strzalek et al which extracted Action View to a separate gem, and also some other improvements.

Summary of changes:

* Reordered the paragraphs from View-Model-Controller to Model-Controller-View, based on how (IMHO) most people think about the structure and hierarchy of the framework and their code in it.
* Added references to ActionView's README in the _View_ paragraph
* Reworded the _Controller_ paragraph to briefly mentioned routing as handled by Action Dispatch, and that both Action Dispatch and Action Controller work together to form the request-handling Action Pack
* Removed paragraph saying Action Pack is coupled with Action View, as this is no longer the case
* Added brief references to Action Mailer and Active Support, since they are both major Rails components. Briefly mentioned in the _View_ paragraph that Action View is often used to generate the body of the email, in addition to the other typical of using to build a response body.
Merge pull request #11986 from fedesoria/patch-3

Warning on doc for assets under lib|vendor not precompiling
Add config to method calls in fixtures.

Allows you to change your configuration for calls to
`table_name_prefix`, `table_name_suffix`, and `pluralize_table_names`.
The default configuration is still ActiveRecord::Base, but you are now
able to change the configuration easily.
Remove whiny_nils config from the rails guides

This option was removed from master.

[ci skip]
Merge pull request #12032 from carolinemota/fixdoc

Remove whiny_nils config from the rails guides [ci skip]