Method align_up

include/jwt/stack_alloc.hpp:121–124

* Rounds up the number to the next closest number * as per the alignment. */

   * as per the alignment.
   */
  constexpr static size_t align_up(size_t n) noexcept
  {
    return (n + (alignment - 1)) & ~(alignment - 1);
  }

private: // data members
  /// Storage