Integration of PDBTBX

[OWissett]

I am one of the maintainers of the pdbtbx crate.

Would it be of interest to people to integrate pdb file processing to this crate?

I am currently not certain exactly how this should be done. I am of the opinion that it would be nice to have a cohesive bioinformatics stack for Rust, and protein structures are an integral part of this stack.

Since this crate is inspired by biopython, I think this would be still in the theme of the crate. I think that potentially having the PDB stuff behind a feature flag would be good as it would keep the crate size down.