feat: Adding from_hashmap for bam Header

[mrvollger]

Hi there,

For bam headers I often want to take the results from bam:Header:to_hashmap manipulate it and create a new header from that hashmap. This is a simple PR that adds a from_hashmap function that allows this.

Cheers,
Mitchell

[coveralls]

Pull Request Test Coverage Report for Build 14738329579

Details

• 0 of 9 (0.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.3%) to 83.282%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/bam/header.rs	0	9	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/bcf/record.rs	1	79.74%
src/bam/pileup.rs	2	81.82%

Totals
Change from base Build 13877817877:	-0.3%
Covered Lines:	2720
Relevant Lines:	3266

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💛 - Coveralls