Revision 3540

Add a Doxygen config file and a Makefile target 'doxy' or 'doxygen' which
generate API documentation (HTML) for libpayload in a 'doxygen' subdirectory.

A 'make clean' will remove this directory again.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Jordan Crouse <jordan.crouse@amd.com>