Rather than adding yet another flag that is almost never useful on its
own, just have --remove-restrictions disable digital signatures. The
operations are still separate in the API.
* Replace --create-from-json=file with --json-input, which causes the
regular input to be treated as json.
* Eliminate --to-json
* In --json=2, bring back "objects" and eliminate "objectinfo". Stream
data is never present.
* In --json-output=2, write "qpdf-v2" with "objects" and include
stream data.
For optional parameter/choices, generate an overloaded config method
that takes no arguments. This makes it possible to convert from a bare
argument to one that takes an optional parameter without breaking
binary compatibility.
Why? The main methods that create them return smart pointers so that
users can initialize them when needed, which you can't do with
references. Returning pointers instead of references makes for a more
uniform interface.
