implement benchmarks and merge join on chan
I've implemented some benchmarks to determine the performance of
the merge join interface given a variety of generated inputs.  The
spacing is logarithmic on input table sizes, because then the
 resulting table ends up as linear on number of records.  I also
 implemented the merge join op for input channels instead of slices
 which should demonstrate its memory efficiency (although it is
 slightly slower).  These are just initial implementations - the
 performance will be improved both by my own investigation and from
 the suggestions of others, which I must now solicit.