OpenSystemsDevelopment / qpdf

Avd xcsv brvtns.

* 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.

Also add stubs for top-level QPDF methods (createFromJSON,
updateFromJSON)

Update getJSON() methods and calls to them

Flatten everything to make it easier to map command-line flags to
json. The old structure was an illusion anyway because there was no
mechanism to enforce that things were in the right place. This also
helps with future flexibility.

Use "file" consistently for specifying a file path. We use "filename"
when adding attachments for a completely different purpose.

Now still have to go through and implement the handlers.

Use named functions rather than just end() for clarity.

All that's left now is input and output handling.

Handle optional choices in addition to required choices. Refactor the
way help options are added to completion to make it work with optional
help choices.