Perf ref: https://gist.github.com/vipulnsward/8209749201dfdd678c97

Tidying "getting started" guide

Section "allowing the update of fields" was now just a general
introduction to the idea of the model (actual updating was two sections
later).  So, merged into the section about validation.

Adding back deprecation require in all.rb

`disable_implicit_join_references=` was only deprecated on `master`,
not with rails 4.0. We can remove it after 4.1

This reverts commit 3c719ead, reversing
changes made to d5c3bf97.

Space is not required for Set-Cookie header

This reverts commit d108672d.

Conflicts:

	activesupport/CHANGELOG.md

Improve Getting Started Guide

Cleanup belongs to tests

removes markdown code markers from displaying in the active record querying guide [ci skip]

simplified logic to calculate number of queries by using assert_queries

Specify request method in guides [ci skip]

Added link to Form Helper article from getting strated [ci skip]

Remove deprecated `ActiveRecord::Base.disable_implicit_join_references=`

Removed unsued deprecation require

Removed deprecated `Rails.application.railties.engines`.

SQL keywords in UPPERCASE

Replaced older rocket sign to new  ":" 

Removed redundant upgrade docs on new cookies.

[ci skip]