Incorporate way of handling Xilinx Coregen ( *.xco ) components
The correct way to handle Xilinx Coregen components is to store the *.xco file in a repository and then generate files using the Xilinx "coregen" tool.
It would be useful to have a way of handling *.xco files in hdmlmake
( it is possible that handling *.xco files is already possible, in
which case it would be good to have this documented )