Add website to client repository

Closes #1567

The main reason I'm not simply merging Annika's PR is because this
way makes it clearer that I'm taking responsibility for all this
code, that it's mostly code I wrote, and also because it makes it
easier to ensure that none of the files have been changed.

(Not that I don't personally trust Annika, but I have something
resembling an obligation to users not to expose them to risks based
on personal trust.)

website/lib/htmlpurifier/HTMLPurifier/ConfigSchema/Builder/ConfigSchema.php

@@ -0,0 +1,44 @@
+<?php
+
+/**
+ * Converts HTMLPurifier_ConfigSchema_Interchange to our runtime
+ * representation used to perform checks on user configuration.
+ */
+class HTMLPurifier_ConfigSchema_Builder_ConfigSchema
+{
+
+    public function build($interchange) {
+        $schema = new HTMLPurifier_ConfigSchema();
+        foreach ($interchange->directives as $d) {
+            $schema->add(
+                $d->id->key,
+                $d->default,
+                $d->type,
+                $d->typeAllowsNull
+            );
+            if ($d->allowed !== null) {
+                $schema->addAllowedValues(
+                    $d->id->key,
+                    $d->allowed
+                );
+            }
+            foreach ($d->aliases as $alias) {
+                $schema->addAlias(
+                    $alias->key,
+                    $d->id->key
+                );
+            }
+            if ($d->valueAliases !== null) {
+                $schema->addValueAliases(
+                    $d->id->key,
+                    $d->valueAliases
+                );
+            }
+        }
+        $schema->postProcess();
+        return $schema;
+    }
+
+}
+
+// vim: et sw=4 sts=4