Bump BioSequences/FASTX to v3/v2

[banhbio]

Bump BioSequences/FASTX to v3/v2

Types of changes

This PR implements the following changes:
(Please tick any or all of the following that are applicable)

• ✨ New feature (A non-breaking change which adds functionality).
• 🐛 Bug fix (A non-breaking change, which fixes an issue).
• 💥 Breaking change (fix or feature that would cause existing functionality to change).

📋 Additional detail

This PR is to follow the latest BioSequences and FASTX.

The changes are as follows.

• Bump BioSequences/FASTX to v3/v2 and Julia to v1.6.
• Replaced constructor to use undef (Remove the constructor LongSequence{A}(::Integer) BioSequences.jl#146)
• Removed BioSequences.encoded_data. (Update interface to version 3. BioSequences.jl#161)
• Renamed/replaced seqlen with seqsize. (Rollup of a few changes FASTX.jl#85)
• Removed ad-hoc code for windows. (Fix windows newline bug (issue 25) FASTX.jl#28)
• Fixed test.

☑️ Checklist

• 🎨 The changes implemented is consistent with the julia style guide.
• 📘 I have updated and added relevant docstrings, in a manner consistent with the documentation styleguide.
• 📘 I have added or updated relevant user and developer manuals/documentation in docs/src/.
• 🆗 There are unit tests that cover the code changes I have made.
• 🆗 The unit tests cover my code changes AND they pass.
• 📝 I have added an entry to the [UNRELEASED] section of the manually curated CHANGELOG.md file for this repository.
• 🆗 All changes should be compatible with the latest stable version of Julia.
• 💭 I have commented liberally for any complex pieces of internal code.

[jakobnissen]

CI seems OK. It fails on Windows but there is a TODO in the code that mentions this failure so it's probably not this PRs fault.

I'll review it closer in a few hours, then I'll merge. Let's make an issue on the Windows failure so we don't lose track of it - perhaps you can track that bug down?

[jakobnissen]

On a second look, it looks like this fix is deleted in the PR?

[banhbio]

Thanks for checking.
I mistakenly thought that the windows bug was already fixed in FASTX.jl.
I need to revert this change.