ZF-2849: Refactor Zend_Config_Ini for readablility

Description

Following ZF-2843, it's clear that Zend_Config_Ini could be refactored to make the code more understandable and easier to maintain.

Comments

First attempt at a clean up. This improves the comments and adds new functions: _loadIniFile(), _loadAllSections() and _loadSection(). Most significantly __construct() is much reduced and so hopefully easier to understand.

This is the full Ini.php file for the first attempt at refactoring Zend_Config_Ini. It may be easier to see the improvements, by looking at the result.

Tidied up in svn r14415.