Support of incremental updates? #308

Hi,

Is there any plan to add 'incremental updates' feature?
Is it something that is already WIP? Or is it not planned at all?

There is a PR here #112, maybe you could use it as a base to start from.

Incremental updates is an important feature that will allow, among others:

• signing an already-signed document
• properly adding signature's revocation information to achieve LTV (Long Term Validation) for signatures