Use rust life times instead of Rc<>

[fd]

@fschutt Are you okay If I attempt to refactor the library such that PageRef and LayerRef types actually use rust life times instead of Rc<>? This would obviously be a breaking change but I believe it would more accurately communicate mutability and ownership of the referenced data.

[fschutt]

You can do it, but it would likely be a waste of time, see https://github.com/fschutt/printpdf/issues/73#issuecomment-712794370

I'll refactor the API properly in the next version anyway, so the PageRef and LayerRef classes will be removed.

[fd]

Yeah I saw you wanted to do a rewrite in a few years (aka. not today). My immediate goals are:

• removing the Pdf{Document,Page,Layer}Reference types and have the api use regular references
• model the XObject references API more like PDF. (eg: add XObject to doc and get XObjectRef, Add XObjectRef to page and get resource name, use resource name to render image). This would allow image stream deduplication and soft masks to be implemented.

These changes could be a stepping stone to a more convenient v2 API.

[fschutt]

ok, go ahead if you want