bam IO logic

1. write a bam reader that can yield a pairs of reads in bam/sam format
2. write a bam sampler that can output an array of pairs of reads size from the bam reader
3. write a bam writer that can add pairs of reads in bam/sam format to a bam file
4. write a function that write pairs of reads in SAM/BAM format into the right bam files depending on the size of the pair of reads using the read_bam, the write_bam function and the output of the classifier function