update sourmash sig export to export to CSV

[ctb]

https://github.com/dib-lab/2020-ibd/blob/master/scripts/sig_to_csv.py

perhaps do this for import too?

[taylorreiter]

It would be really great if a script like this could be integrated into sourmash sig, with command line parameters to include or remove abundances. Also would be handy to figure out how to deal with multiple kmer sizes -- does ksize become a column where this information is recorded (probably best practice) vs. ksize needing to be selected with a command line param a la compare

[taylorreiter]

I use csvs all the time to R things like make upset plots, run random forests, and generate rarefaction curves

upset plots: https://github.com/sourmash-bio/sourmash/issues/1234#issuecomment-1055709316 upset plots: https://github.com/Arcadia-Science/2022-prjna853785-sourmash/blob/main/notebooks/20220812-visualize-sourmash-signature-intersect.ipynb rarefaction curves: https://github.com/Arcadia-Science/2022-mtx-not-in-mgx-pairs/blob/ter/specaccum/scripts/calc_rarecurves.R rarefaction curve viz: https://github.com/Arcadia-Science/2022-mtx-not-in-mgx-pairs/blob/ter/specaccum/notebooks/20220929-visualize-most-converged-rarefaction-curves.ipynb

[ctb]

thought: probably want to upgrade import as well, so that it can take in the same format as export!