Add document ID to trailer for PDF/X

[bousquet]

Adds a default trailer that includes a document ID consisting of two random hex values. This is used for PDF-X compatibility but does not negatively affect other PDF formats. A :trailer option can also be passed in during initialization which can override the default.

Also added basic specs or the PDF::Core::DocumentState class which had none.

[packetmonkey]

I'm not comfortable by default including random information in a document. That means if we run the same PDF generation code twice we would get different PDFs out the other side.

I think I am ok requiring someone to set the trailer on document initialization to set an ID if they plan on kicking out a PDF/X document. We could also after the merge discuss possibly creating a Prawn::PDFX class that does the PDF/X initialization for you and can do other things like try to ensure CMYK only images and what-not.

[bousquet]

Ok, I think that's a good point. I've removed the default_trailer and left it as the empty hash it was before, but left in the option to pass the trailer in via the options.

[packetmonkey]

Some minor tweaks and I think this will be ready to merge.

1. I think we can remove the added require "secure random" as we aren't adding a random ID anymore.
2. Your describe "default trailer" do test isn't describing the default trailer, it's describing a trailer that was set. I think we if we rename the block describe explicit trailer it would be fine
3. We should add a test to in fact ensure the trailer without any extra parameters is initialized correctly.

Once this gets merged we can add a changelog file to the repo so we can start to track changes in pdf-core as opposed to prawn.

Thanks!

[bousquet]

I have adjusted the tests and removed the securerandom call. Good catch.

[packetmonkey]

I'm good with this update. thanks for the pull request! Once @practicingruby gives me access to the contributors group you will get commit access to the repositories because you had a pull request merged. here are the details.

Thanks again! Hopefully we can wrap up and give you easy access to all the PDF/X features your heart desires ❤️

[packetmonkey]

You have been added to the contributors group, thanks again!