Revised the fastpos code. It now uses the slightly faster

Revised the fastpos code. It now uses the slightly faster
table-based version from LZMA SDK 4.57. This should be
fast on most systems.

A simpler and smaller alternative version is also provided.
On some CPUs this can be even a little faster than the
default table-based version (see comments in fastpos.h),
but on most systems the table-based code is faster.