Provide a public-facing parse function

This should allow devs using the library to retrieve HTML pages through other methods, if they wish, and parse them using the OpenGraph library.

OpenGraph.php

@@ -77,6 +77,14 @@ static public function fetch($URI) {
         return false;
     }
 	}
+
+	static public function parse($HTML){
+		if ( empty( $HTML ) ){
+			return false;
+		}
+		$response = mb_convert_encoding($HTML, 'HTML-ENTITIES', 'UTF-8');
+		return self::_parse($response);
+	}
 
   /**
    * Parses HTML and extracts Open Graph data, this assumes