fixed README, fixed required/optional (optional is default)

Author: digitalkaoz

README.md

@@ -2,13 +2,17 @@
 
 ## Usage
 
-  $json = json_decode($input_json);
-  $schema = json_decode($input_schema);
-  $result = JsonSchema::validate($json, $schema);
-  
-  if ($result->valid) {
+```php
+<?php
+
+$json = json_decode($input_json);
+$schema = json_decode($input_schema);
+$result = JsonSchema::validate($json, $schema);
+
+if ($result->valid) {
     die('success!');
-  }
-  else {
+}
+else {
     die('fail...');
-  }
+}
+```

libs/JsonSchema.php

@@ -169,7 +169,7 @@ static function checkProp($value, $schema, $path, $i = '', $_changing = false) {
     }
     // verify optional values
     if (is_object($value) && $value instanceOf JsonSchemaUndefined) {
-  	  if ( isset($schema->optional) ? !$schema->optional : true) {
+  	  if ( isset($schema->required) ? !$schema->required : true) {
 	    self::adderror($path,"is missing and it is not optional");
 	  }
     }