Add -l/--linearize option

[Scriptim]

From https://sno.phy.queensu.ca/~phil/exiftool/TagNames/PDF.html:

2. All metadata edits are reversible. While this would normally be considered an advantage, it is a potential security problem because old information is never actually deleted from the file. (However, after running ExifTool the old information may be removed permanently using the "qpdf" utility with this command: "qpdf --linearize in.pdf out.pdf".)

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https://gist.github.com/hubgit/6078384