add MapperContext
add MapperContext

handles generating a multiprocessing.Pool and closing it when done

probcomp/crosscat,probcomp/crosscat,mit-probabilistic-computing-project/crosscat,mit-probabilistic-computing-project/crosscat,fivejjs/crosscat,probcomp/crosscat,probcomp/crosscat,fivejjs/crosscat,probcomp/crosscat,probcomp/crosscat,probcomp/crosscat,mit-probabilistic-computing-project/crosscat,mit-probabilistic-computing-project/crosscat,mit-probabilistic-computing-project/crosscat,fivejjs/crosscat,fivejjs/crosscat,mit-probabilistic-computing-project/crosscat,mit-probabilistic-computing-project/crosscat,fivejjs/crosscat,fivejjs/crosscat,fivejjs/crosscat,probcomp/crosscat