add set_region to RegionLimitedBamReader

in case you want to hop to a different region later without having to
reopen the bam / reload the index
bam2cfg: add --verbose/-V option

when set, information about outliers that are removed is displayed
add make_unique_ until we can use c++14
add MultiRegionLimitedBamReader

reads from a bunch of regions in sequence
add --skip and --regions options to bam2cfg

regions isn't really useful yet. i'll try to come back later and make
it randomly sample from the regions