FEATURE REQUEST: Improve seqinfo(<BamFile>) to return the genome assembly associated with each sequence

[hpages]

Right now seqinfo(<BamFile>) returns a Seqinfo object with no genome information, even though that information is available in the file (the genome assembly is specified via the AS tag found in the @SQ header lines).

See Bioconductor/GenomeInfoDb#105 (comment) for some context.

I'll try to come up with a PR that fixes that.