Updated articles on bidi topics

The following articles have been updated and reviewed by the Internationalization Working Group. If you have additional comments, please send them using the “Leave a comment” link at the bottom right of the page.

How to use Unicode controls for bidi text
see the changes on github

Unicode controls vs. markup for bidi support
see changes on github

CSS vs. markup for bidi support
see changes on github

Changes include the following:

* added a quick answer
* removed background sections now that we have other articles that deal with that information (pointed to those)
* clarified the distinction between structural/block markup and inline markup wrt control character usage in a new section
* expanded the section on inline issues to take into account HTML5-related developments
* introduced concept of isolation, including RLI/LRI/FSI/PDI
* removed out of date references and quotations
* introduced the concept of tightly-wrapping all opposite-direction phrases from the HTML article
* basically rewrote everything to make it cleaner, clearer and more snappy
* replaced outdated spec links and quotes
* added reference to polyglot
* pointed to the HTML5 rendering section rather than providing a CSS template (which was out of date) in the document