Add toy SAM/BAM files, add test for bam_parser.parse_bam_header

[nwiltsie]

This adds a functional test for the parse_bam_header function.

For testing data I copied the tiny sample SAM file from the samtools GitHub repository (I added the origin link as a @CO record). I also created a duplicate with a @RG record, as that's the only thing parse_bam_header actually looks for! I turned the two SAM files into BAM files and commited the lot of them.

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[yashpatel6]

Looks good!