Update to use skbio's subsample_multinomial
Remove unused IUPAC_DNA* imports
Merge branch 'master' into sub-multi
Update to use latest skbio subsampling API.
Merge pull request #1470 from ElBrogrammer/sub-multi

Update to use scikit-bio's subsampling with replacement
update split_libaries to use skbio degen expander
Remove unused imports
Merge pull request #1472 from ElBrogrammer/skbio-iupac

update to use skbio's degeneracy expander