Signature dictionary entries support

[eduperottoni]

Hey, @MatthiasValvekens!

According to ISO3200-2 (2020), there are many entries in the PDF's signature dictionary (table 255), e.g. /R, /M, /Name, /Reason, /Location, /Prop_Build, /Prop_AuthTime, /Prop_AuthType, /ByteRange and others. On the other hand, in pyHanko's API, we only have some of them exposed in the SignatureObject, being them: timestamp, subfilter, name, location, reason, app_build_props and bytes_reserved.
I know it's easy to inherit this class and create new entries to be part of my signature dictionary (and I did for /Prop_AuthTime and /ContactInfo entries, for example). However, is there any reason to pyHanko's lack of support to this entries?

Thank you!

[MatthiasValvekens]

Almost all of these are supported, actually (see e.g. #195 for the PR that adds /Prop_Build support).

The ones that aren't supported (e.g. /R and some of the /Prop_XYZ ones) aren't included because nobody asked so far :). Feel free to submit a PR.

[eduperottoni]

Oh, I forgot to notify before to link here, but the PR #314 was done in order to solve this issue.