fix: Workaround Non-Threadsafe Use of Rc in bam::record::Record

[jch-13]

Hey all, this is an attempt to work around #293 (for context please see the discussion there).

I simply removed the reference counted reference to HeaderView from BAM Records and impl'ed genome::AbstractInterval on a wrapper type around &Record and &HeaderView. This wrapper type can be constructed like this:

let header = bam_reader.header().clone();
for record in bam_reader.records() {
    let mut rec = record.unwrap();
    // `.contig()` is a member of the `genome::AbstractInterval` trait
    let contig = rec.supply_header(&header).contig();
}

This is not exactly elegant and I don't know the use cases that made references to headers necessary in the first place, so please let me know if this workaround is viable at all.

Edit: I've removed Rc wrappers around HeaderViews as well since I doubt they were actually needed. unsafe Send impls for Reader and Writer had to be removed too because they were unsound.
I hope this does not break a lot of code and I'm not missing anything obvious here... :)

[coveralls]

Pull Request Test Coverage Report for Build 1789725128

• 13 of 21 (61.9%) changed or added relevant lines in 3 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 94.766%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/bam/buffer.rs	5	8	62.5%
src/bam/record.rs	0	5	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/bam/record.rs	6	79.68%

Totals
Change from base Build 1484386366:	-0.03%
Covered Lines:	11515
Relevant Lines:	12151

---

💛 - Coveralls

[johanneskoester]

The use case was to make it convenient to conduct header-requiring operations without having the reader at hand (e.g. in a larger codebase, where passing on the reader would make things unnecessarily complicated). @jch-13, you thing Arc would be an alternative?