Refactor some CUDA compatibility #ifdefs into a separate header
Switch between debug (default) and optimized builds with OPTIMIZE=1 option to make.  Makes a 50% difference in speed.
Add some heuristics to the Optimize() method to force it to favor small
block sizes.  This improves performance when evaluating many PDFs
at the same time.
Merge branch 'master' of github.com:mastbaum/sxmc