updated abundance filtering part
1. using filter-abund.py to do the filtering(trimming), remove the region on reads, that has low abundance(<2)
2. using tallymer to test if the remaining reads have any unique k-mers, get the number of reads with unique k-mers.
They are not exactly same, since trimming will still leave some unique k-mers in middle of reads???
hash size =1e8 didn't work. (too small hashtable to get reasonable fpr), but now 1e9 and 1e10 have similar performance.(no big difference in number of remaining reads)