installation instructions update
Merge pull request #1619 from antograssiot/3.0_installation

3-0 installation instructions update
[fr] follow #1614

3.0 correct link to ProGit book
[fr] follow c6547b5

Update info regarding return value from authenticate provider.
[fr] follow #1613

Shell::param()
[fr] follow #1610

Fix eg. code.
[fr] follow #1611 & follow en

3.0 doc correct model link on index page
[fr] follow 62eece1

Fix example code.
[fr] follow #1602

table-objects, fix deleteAll example
[fr] follow #1601

Update docs for App::objects() removal.
[fr] rearrange logging to follow en
[fr] update files from root folder

follow en version
Fixes broken link to Ruby Cells.

Now links to GitHub project page for the gem.
Merge pull request #1623 from alecho/patch-2

Fixes broken link to Ruby Cells.
Fix typo
Removed notices about ``--stderr``

May be I missunderstood this, but acording to @lorenzo

https://github.com/cakephp/cakephp/pull/3521#issue-33758906

> With this merged, we have no longer need for running tests with --stderr and we can safely use phpunit 4.1
Fixed broken link to PHP's json_encode
Fix typo.

Fixes #1627