split-pdf: extract splitter into scripts/ and switch backend to pypdf#15

nsmiller2501 wants to merge 3 commits into

scunning1975:mainscunning1975/MixtapeTools:mainfrom

nsmiller2501:followup/split-pdf-pypdfnsmiller2501/MixtapeTools:followup/split-pdf-pypdfCopy head branch name to clipboard