Change default probability max and increment for Fenwick/MTF.

This is what most users of these models were using; change so that
the stand-alone benchmarks are consistent with the users.

The RangeCoder decode seems to be rather slow, probably because of
the division; the deferred summation decode is fast, and it replaces
the division with a shift.
Use deferred summation model for bwtc -1 through -5 for moar speed.

Sacrifices some compression, but presumably if you're using -1 and -5
you want the blazing-fast decode speed.
Update benchmark results for sample5.