Add "other" field to Page

[frankfralick]

This PR adds a field called "other" to Page, enabling access to the various optional entries that can be present. This also adds an example "other_page_content" as well as an example file to use with it "example_annotation.pdf" that demonstrates finding text that has been struck through.

[s3bk]

I think Annots should be added as a field later. But for now this will work just fine.

[frankfralick]

Thanks. I will hopefully be at a point in the next month where I'm going to need to deal with a much broader set of the annotation types than I currently do. If you are open to it I would like to add a field for it and type similar to how Resources is. Before I do a lot of work I will show you what I'd propose on Zulip. Also, do you have any idea when you might publish a new version of this repo to crates.io?