KEGG db formatting process should allow passing in directory of pep files

[madeline-scyphers]

When downloading the KEGG db, the .pep files aren't pre concatenated and users currently have to concatenate them themselves. It wouldn't be hard to do that for them if they supply the location where all of the individual pep files are.

Also, it seems that because of header file changes in KEGG, it might not be as easy at concatenating pep files anymore. So providing a script to do it for people, would be best.

See https://github.com/WrightonLabCSU/DRAM2-Archived/blob/aa663ee8bc220774ebb97b0473431f1c52d5b2c4/extra/kegg_tools/format_kegg.py
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