Allow piping to standard output

[odeke-em]

It would be nice to add ability to pipe concatenated output to standard output This would make it easy for a user to use pdfcat with a whole range of Unix utilities

$ pdfcat lec*.pdf -piped | drive pull --piped ece410Lectures.pdf
$ pdfcat lec*.pdf -piped | openssl enc -aes-256-cbc -salt -kfile passPhraseFileOrDevice | drive push --piped encryptedLectures.pdf

Thanks!

[odeke-em]

Or any variant of args for standard output , --stdout. Nice utility btw!