OpenSystemsDevelopment / qpdf

In internal code and examples, replace calls to getObjectID() and
getGeneration() with calls to getObjGen() where possible.

This is safer than getObjectID() and getGeneration() for many uses.

Windows fix: QPDFObject::ParserCallbacks::terminateParsing() was not
declared with QPDF_DLL.

Explicitly state how QPDF handles empty passwords when writing files.
Apparently some libraries treat the empty string as the owner password
as an instruction to generate a random password.

Remove const qualifier from getTypeCode and get getTypeName methods of
QPDFObjectHandle, make them work properly for indirect objects, and
exercise them much better in the test suite.

fopen was previuosly called wrapped by QUtil::fopen_wrapper, but
QUtil::safe_fopen does this itself, which is less cumbersome.

Add QUtil::hex_encode to encode binary data has a hexadecimal string,
and use it in place of sprintf where possible.

Change object type Keyword to Operator, and place the order of the
object types in object_type_e in the same order as they are mentioned
in the PDF specification.

Note that this change only breaks backward compatibility with code
that has not yet been released.

Add virtual methods to QPDFObject, wrappers to QPDFObjectHandle, and
implementations to all the QPDF_Object types.

This method allows parsing of the PDF objects in a content stream or
array of content streams.

These object types are to facilitate content stream parsing.

With newer encryption formats, it is no longer possible to recover the
user password using the owner password.

When preparing the trailer for writing to the new file, trim a copy of
the trailer instead of the original file's trailer.

Also add copyright notice to a few public headers that were missing
one.

Original code was written before we could shallow copy objects, so all
the filtering was done by suppressing the output of certain keys and
replacing them with other keys.  Now we can simplify the code greatly
by modifying shallow copies of dictionaries in place.

Read and write support is implemented for /V=5 with /R=5 as well as
/R=6.  /R=5 is the deprecated encryption method used by Acrobat IX.
/R=6 is the encryption method used by PDF 2.0 from ISO 32000-2.

Test cases added in a future commit since they depend on /R=6 support.

All version operations are now fully aware of extension levels.

Allowing users to subclass InputSource and Pipeline to read and write
from/to arbitrary sources provides the maximum flexibility for users
who want to read and write from other than files or memory.

Move object parsing code from QPDF to QPDFObjectHandle and
parameterize the parts of it that are specific to a QPDF object.
Provide a version that can't handle indirect objects and that can be
called on an arbitrary string.

A side effect of this change is that the offset used when reporting
invalid stream length has changed, but since the new value seems like
a better value than the old one, the test suite has been updated
rather than making the code backward compatible.  This only effects
the offset reported for invalid streams that lack /Length or have an
invalid /Length key.

Updated some test code and exmaples to use QPDFObjectHandle::parse.

Supporting changes include adding a BufferInputSource constructor that
takes a string.

InputSource, FileInputSource, and BufferInputSource are now top-level
classes instead of privately nested inside QPDF.

Add --copy-encryption and --encryption-file-password options to qpdf.
Also strengthen test suite for copying encryption.  The strengthened
test suite would have caught the failure to preserve AES and the
failure to update the file version, which was invalidating the
encrypted data.

Method to copy encryption parameters from another file.  Adapted from
existing code to copy encryption parameters from the original file.