Support rewriting document contents on save changes

[pcorless]

The library has supported incremental updates since annotation support was added. Incremental updates is an important feature in PDF for tracking changes and allowing for quick efficient updates. However as precursor to support redaction annotations a new API needs to be created to allow the rewriting of any object in the document that has changed. In the case of redaction's and potentially other publishing cases it is not desirable to use increment updates as the original data would still be available in the PDF file stream.

This ticket will just cover the creation of an API and accompanying data structures to support updated changed objects in PDF file and rewriting the file in it's entirety.

• append the Document API saveToOutputStream() to have a new parameter to specify either incremental update or update.
• the existing state manager can be leveraged to grab the update objects that need to be written.
• handle compressed object stream
• device a scheme to update or rewrite xref streams and tables with the new object offset.
• encrypted document will needs some specially handling. I can't remember if the keys are symmetric. If they are, then great this should be relatively straight forward. Similarly more research is needed to consider the different encryption standards available.

[pcorless]

Marking as closed. Will update ass needed if redaction related changes are needed.