Add type-safe wrapper around realpath

MD_STD.php

@@ -34,6 +34,22 @@ public static function file_get_contents(string $filename):string {
 
     }
 
+    /**
+     * Returns the real path of a relative file path. Throws an error rather than
+     * returning the default false.
+     *
+     * @param string $path File path to convert.
+     *
+     * @return string
+     */
+    public static function realpath(string $path):string {
+
+        $output = realpath($path);
+        if (!is_string($output)) throw new MDFileDoesNotExist("The file {$path} does not exist or is not readable.");
+        return $output;
+
+    }
+
     /**
      * Gets contents of a folder.
      *