Cython implementation of LFSR jumpahead() functions.
Fix SHR3 pure Python jumpahead function -- definition of _SHR3_MATRIX.
This was broken in rev 6a050631402e3a3322155d9c364e19477a042916.
Superficial style change.
Fix unit tests for LFSR jumpahead() functions.
Pure Python MWC jumpahead functions.