diffhash updates

[olgabot]

Adds option for --diff_hash_with_abundance to account for abundances of hashes when doing differential hash expression. Also actually adds some documentation

PR checklist

• [x] This comment contains a description of changes (with reason)
• [x] If you've fixed a bug or added code that should be tested, add tests!
• [x] Ensure the test suite passes (nextflow run . -profile test,docker).
• [x] Make sure your code lints (nf-core lint .).
• [ ] ~Documentation in docs is updated~
• [x] CHANGELOG.md is updated

Learn more about contributing: CONTRIBUTING.md

[olgabot]

Punting writing docs to https://github.com/czbiohub/nf-predictorthologs/pull/35 where there's actually a usage section added

[olgabot]

sourmash search results are still empty, investigating

(base)
 Mon 27 Apr - 08:13  ~/code/nf-predictorthologs--olgabot/diffhash-v2   olgabot/diffhash-v2 ✔ 1☀ 
  head results/sourmash/search/*
==> results/sourmash/search/hash-1000205953012439013.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-1495932068113268597.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-15007113384290734478.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-1546493864503921709.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-1744843537079830884.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-2617310514365118384.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-3528776232794193794.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-4122771730240801637.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-691226190705356132.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-691738281129090084.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-741677291885817446.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-8035688914585273533.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-807635103818932299.csv <==
similarity,name,filename,md5

==> results/sourmash/search/hash-926359818839500271.csv <==
similarity,name,filename,md5