Jtag SLD Hub now officially documented

Really nice. It seems to be neccessary to browse MF user guides for updates from time to time. I also see a late echo to previous user requests. Thanks!

To my opinion, a documentation of sld_hapi.dll interface would perfectly supplement V2.0 ug_virtualjtag.

@Rysc: There are many possible applications, I think. As an example, I'm just now finishing a design, that uses a Source&Probe instance included with the final FPGA image as test interface, operated through a PC user application. You either need an interface to the Quartus JTAG protol stack or have to understand the virtual JTAG protocol at the wire level to access VJTAG instances in the design.

I regard the rich VJTAG infrastructure provided by Quartus and Altera FPGA as an important product feature. With some support, it could be further opened to user applications.