Add type-safe wrapper around strtotime, removing ability for second

param.

MD_STD.php

@@ -154,6 +154,21 @@ public static function json_encode(array $value, int $options = 0, int $depth =
 
     }
 
+    /**
+     * Type-safe wrapper around strtotime().
+     *
+     * @param string $datetime String to convert.
+     *
+     * @return integer
+     */
+    public static function strtotime(string $datetime):int {
+
+        $output = strtotime($datetime);
+        if ($output === false) throw new MDInvalidInputDate("Invalid input date {$datetime}.");
+        return $output;
+
+    }
+
     /**
      * Wrapper for curling contents from the web.
      *