Add usage examples to ArrayHelper

fixes #35.
Merge pull request #38 from eirslett/document-array-helper

Add usage examples to ArrayHelper
Closes #35
Resetting @since for semver
Remove all traces of JPlatform version class.
Removing JPlatform from intro doc [ci skip]
Removing JPlatform from intro doc [ci skip]
Fixing utilities composer.json [ci skip]
Merge branch 'master' of github.com:joomla/joomla-framework