Ignoring parts of a file: update for WordPressCS 3.0.0
* Remove problematic words from the text.
* Change project references from "WPCS" to "WordPressCS".
* Change the order of the page: move the "When to use" section up to above the "WordPressCS native ignore comments" section.
* Rewrite the introduction of the "WordPressCS native ignore comments" section, emphasizing that support has been removed.
* Hide the details of the old WPCS native ignore comments behind a fold-out section.
This means the information is still available for people upgrading from really old versions of WordPressCS, just less "in your face".
* Minor other textual tweaks.