feat: Add ability to fetch number of sequences and I-th sequence from FAI index

[jamorrison]

faidx.c has two functions for retrieving the number of sequences in the FAI index (faidx_nseq) and the name of the I-th sequence (faidx_iseq). Previously these two functions weren't accessible through rust-htslib. I've added a function to access each of these into the faidx module.

This is my first PR for rust-htslib, so let me know if there are any things I can improve upon in my code!

[jamorrison]

@johanneskoester Would mind reviewing my PR? Thank you!

[johanneskoester]

Thanks! I would rename the functions a bit, see below.

[jamorrison]

Thanks @johanneskoester for the comments. I committed your suggested name changes.

[brentp]

I need this functionality, anything holding up the PR?

[brainstorm]

I need this functionality, anything holding up the PR?

Hi @brentp, code LGTM and CI passes (allowed the CI run yesterday). I'd guess that perhaps a matching test might be what's holding this from getting merged? Up to Johannes! ;)

[brentp]

Thanks @brainstorm .
@jamorrison , you can take my tests nearly verbatim from #381

[jamorrison]

Thanks @brentp for the test code!

@johanneskoester I've added added tests for the two functions in the PR. Let me know if there's further work that needs to be done to wrap up this PR.

[johanneskoester]

Awesome guys, thank you! In general: I often miss github notifications because I get so many. Just ping me via discord, twitter or email if I fail to respond in time.