Add support for bam_aux_update_str(), bam_aux_update_int(), bam_aux_update_float(), bam_aux_update_array()

[ghuls]

Add support for HTSlib bam_aux_update_str(), bam_aux_update_int(), bam_aux_update_float(), bam_aux_update_array:
samtools/htslib#694

This allows updating an existing aux tag instead of having to do: remove_aux => push_aux and also keeps that aux at the same position instead of moving it to the end.

[ghuls]

@dlaehnemann Can you look at this pull request?