Render a block diagram of the xilinx_bitstream.ksy file into the Sphinx Docs

[mithro]

@kc8apf put together a Kaitai Struct language description of the Xilinx Bitstream format here -> https://github.com/SymbiFlow/prjxray/blob/master/docs/xilinx_bitstream.ksy

It would be great to render in our document as the file as shown here -> http://formats.kaitai.io/edid/index.html

KSY can be converted to GraphViz .dot format. Sphinx has an extension for rendering GraphViz files.

KSY can be converted to Python code and Sphinx can read Python code. That could be a useful method for getting the stuff into Sphinx too.