OpenSystemsDevelopment / qpdf

* 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.

There are no automated tests yet, but committing work so far in
preparation for some refactoring.

These mean to leave the original values alone. This is needed for
reconstructing streams from JSON given that the stream data and stream
dictionary may appear in any order in the JSON.

I decided these were confusing and inconsistent with how JSON works.
They muddle the API rather than improving it.

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

The last offset is irrelevant to not being able to find /Root.

When an empty string was passed to replaceStreamData, the code was
passing a null pointer to memcpy. Since a 0 size was also passed, this
was harmless, but it triggers sanitizer errors. The code properly
handles a null pointer as the buffer in other places.

Call the parent container's item method before calling the child
item's start method so we can easily know the current nesting level
when nested items are added.

moddify -> modify. Also carefully spell checked all remaining keys by
splitting them into words and running a spell checker, not just
relying on visual proofreading. That was the only one.

Not fully exercised in this commit

Also refine the herustic for deciding whether to use hexadecimal
notation for a string.

Update getJSON() methods and calls to them

This script was used on test data:

----------
#!/usr/bin/env python3
import json
import sys
import re

def json_dumps(data):
    return json.dumps(data, ensure_ascii=False,
                      indent=2, separators=(',', ': '))

for filename in sys.argv[1:]:
    with open(filename, 'r') as f:
        data = json.loads(f.read())
    if 'objectinfo' not in data:
        continue
    trailer = None
    to_sort = []
    for k, v in data['objectinfo'].items():
        if k == 'trailer':
            trailer = v
        else:
            m = re.match(r'^(\d+) \d+ R', k)
            if m:
                to_sort.append([int(m.group(1)), k, v])
    newobjectinfo = {x[1]: x[2] for x in sorted(to_sort)}
    if trailer is not None:
        newobjectinfo['trailer'] = trailer
    data['objectinfo'] = newobjectinfo
print(json_dumps(data))
----------

The following script was used to adjust test data:

----------
#!/usr/bin/env python3
import json
import sys
import re

def json_dumps(data):
    return json.dumps(data, ensure_ascii=False,
                      indent=2, separators=(',', ': '))

for filename in sys.argv[1:]:
    with open(filename, 'r') as f:
        data = json.loads(f.read())
    if 'objects' not in data:
        continue
    trailer = None
    to_sort = []
    for k, v in data['objects'].items():
        if k == 'trailer':
            trailer = v
        else:
            m = re.match(r'^(\d+) \d+ R', k)
            if m:
                to_sort.append([int(m.group(1)), k, v])
    newobjects = {x[1]: x[2] for x in sorted(to_sort)}
    if trailer is not None:
        newobjects['trailer'] = trailer
    data['objects'] = newobjects
print(json_dumps(data))
----------

This commit just changes the order in which fields are written to the
json without changing their content. All the json files in the test
suite were modified with this script to ensure that we didn't get any
changes other than ordering.

----------
#!/usr/bin/env python3
import json
import sys

def json_dumps(data):
    return json.dumps(data, ensure_ascii=False,
                      indent=2, separators=(',', ': '))

for filename in sys.argv[1:]:
    with open(filename, 'r') as f:
        data = json.loads(f.read())
    newdata = {}
    for i in ('version', 'parameters', 'pages', 'pagelabels',
              'acroform', 'attachments', 'encrypt', 'outlines',
              'objects', 'objectinfo'):
        if i in data:
            newdata[i] = data[i]
print(json_dumps(newdata))
----------

Testing json against schema requires an in-memory copy, so do it only
when requested by the test suite.

We used to have to do that, but for quite some time, the code that
gets images has no longer required it.