How to add my own algorithm to gnupg?

[Calvin]

Hi, there,
Please reply to me explicitly for I'm in none of above mail list.
Thanks.

There is a line in gnupg "Feature" page, which says, "Easy
implementation of new algorithms using extension modules."

But I can't find where to configure to use my own algorithms. And what's
the "extension modules" mean?

Do I need to add my algorithm module to source code of gnupg and 
rebuild it? Or there is some easier way, just follow a specific
interface in my module and register it into gnupg with some
configuration file? Or the 3rd way?

Thanks for help.

Best regards,
Calvin