Altered configuration for improved compression.

Added changes I made some time ago to the Zopfli configuration.
Compression is improved, especially for larger files.

- Setting blocksplittingmax to 0 (zero) in util.c seems to improve
compression markedly for larger files. I have not yet come across a
case of ”extreme results that hurt compression on some files”.

- The changes in util.h trades memory usage and speed for better
compression.