Allow chaining in the addCrumb method

For convenience I think it might be valuable to allow addCrumb (and possibly other similar functions) to return $this to permit chained calls such as this:

    $this->Html->addCrumb('Admin', '/admin')->addCrumb('Blogs', '/admin/users')->addCrumb('Add');

as opposed to the considerably more verbose version that needs to be used now:

    $this->Html->addCrumb('Admin', '/admin');
    $this->Html->addCrumb('Blogs', '/admin/users');
    $this->Html->addCrumb('Add');

I'm not sure if this violates some API conventions for helpers but it does seem rather more convenient to work with to me.
Update HtmlHelper.php

Updated documentation to include the chained $this return
Update doc blocks to not be lies.
Removed arbitrary restriction on crud operations. Added some comments to explain parameters to mapActions() better.
Merge pull request #3146 from sam-at-github/baseauthorize-crud

Removed arbitrary restriction on crud operations in BaseAuthorize.
Expose canUseMemory

This lets Fixture be used to create an actual persistent table with InnoDB engine instead of MEMORY.
on `cake acl delete <>` delete all matching records. Makes more sense than deleting one of possibly many.
Fixed CS issues. Fixed bug - added missing condition to find.
No array short syntax in 2.4\!
Merge pull request #3156 from sam-at-github/acl-shell-delete-all

Make `cake acl delete <acl-object>` delete all matching records.
Merge pull request #3147 from planardothum/persistent-fixture

Expose canUseMemory
Correct docblock.

Refs #3147
Remove $reponse param of Dispatcher::_invoke().

Use controller's $response property by default.
Merge pull request #3152 from ADmad/2.5-controller-invoking

2.5 controller invoking
Merge branch 'master' into 2.5
Merge branch '2.5' of github.com:cakephp/cakephp into 2.5
Fix yoda condition in File test
Merge pull request #3186 from bcrowe/hotfix-yoda-test

Fix yoda condition in File test
Adds phpunit required version to TestShell "not found" error message.
Merge pull request #3193 from beporter/feature/phpunit-required-version

Adds phpunit required version to TestShell "not found" error message.