[[feature-stackdir]] Allow specifying a specific token type to peek or consume.

This makes it possible to write:

    if (!MCStackdirIOScannerConsume (scanner, t_token,
                                     kMCStackdirIOTokenTypeSpace))
    {
         /* Report syntax error */
    }

instead of:

    if (!(MCStackdirIOScannerConsume (scanner, t_token) &&
          t_token.m_type == kMCStackdirIOTokenTypeSpace))
    {
        /* Report syntax error */
    }