Add help tabs support

Add SettingsPage::getOption() method

It supports dot notation access for deep option structures.

Fix broken PHP 5.3 compatibility caused by short array syntax introdu…

…ced with PHP 5.4

Set `$title` argument default to empty string in `Section::__construct`

Add support for top level admin menu page setup.

There are new fields, `parent_slug`, `icon_url`, `position`, for `SettingsPage` options. Those options closely related to the `add_menu_page()` function arguments and have the same defaults. If `parent_slug` value is `own`, page will be a top level menu.

usage added to readme