fixed bug where first read repeated

the bug happened for acrocentric chromosomes where the first block of
the chr was all GAP so for every random position in the acrocentric
region you woudl get the same read - ie, the first non-acrocentric read
Merge branch 'master' of https://github.com/psudmant/stream_read_pair
Sample 100 pairs at each position to fix insert size bias
Merge branch 'master' of https://github.com/bnelsj/stream_read_pair