Replace FASTA reading/writing with functions from BioFSharp

[gsvgit]

Replace FASTA reading/writing with functions from BioFSharp. If we have some useful functionality, then move it to BioFSharp.

• [ ] Propose to owners of BioFSharp to publish NuGet package. (Post an issue). Propose to help to create packaging scripts.
• [ ] Replace FASTA processing with functions from BioFSharp package. If necessary then move some functions from our project to BioFSharp.