Repair priority filter 2
Added a failed alg. optimisation
Failed attempt to use Image instead of Scatter
Attempt at cythonising persistent class
Clean up length_factor
Don't bother testing PF 3,4,5 - currently unused
Moved before_set_occ to util stats
Test PF2 by default - PF1 is stable and outdated
Always include openings book, just use for P1 move 2
More testing
Lots of little cython optimisations
Change default filter to 2
Make it easy to toggle cython profiling