LFSR taps

I had to fix up the LFSR code in my block benching tool, and this Xilinx document was very useful for figuring out the primitive polynomials for bits > 16.

http://www.xilinx.com/support/documentation/application_notes/xapp052.pdf

Ended up reading about Galois Fields and Évariste Galois...humbling...humbling...