Add README for the extras/ folder.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1530 48356398-32a2-884e-a903-53898d9a118a

extras/README

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+
+HTML Purifier Extras
+    The Method Behind The Madness!
+
+The extras/ folder in HTML Purifier contains--you guessed it--extra things
+for HTML Purifier.  Specifically, these are two extra libraries called
+FSTools and ConfigSchema.  They're extra for a reason: you don't need them
+if you're using HTML Purifier for normal usage: filtering HTML.  However,
+if you're a developer, and would like to test HTML Purifier, or need to
+use one of HTML Purifier's maintenance scripts, chances are they'll need
+these libraries. Who knows: maybe you'll find them useful too!
+
+Here are the libraries:
+
+
+FSTools
+-------
+
+Short for File System Tools, this is a poor-man's object-oriented wrapper for
+the filesystem. It currently consists of two classes:
+
+- FSTools: This is a singleton that contains a manner of useful functions
+  such as recursive glob, directory removal, etc, as well as the ability
+  to call arbitrary native PHP functions through it like $FS->fopen(...).
+  This makes it a lot simpler to mock these filesystem calls for unit testing.
+
+- FSTools_File: This object represents a single file, and has almost any 
+  method imaginable one would need.
+
+Check the files themselves for more information.
+
+
+ConfigSchema
+------------
+
+ConfigSchema is the next-generation configuration validation system for
+HTML Purifier, built off of the original HTMLPurifier_ConfigSchema. When
+complete, it will be used to generate schema files which will then be used
+to enforce values set to HTMLPurifier_Config.