Updating extraction script for Satz.

Now changing "prpr" column to "dc" to bring in line with OKsolver.
Adding comments interpreting the old satz output in terms of the extraction statistics.
Merge branch 'satz_extraction_comment' of git://github.com/MGwynne/oklibrary
Correction: no "match with the OKsolver".
Removed superfluous $-symbols.
Removed superfluous comments.