OpenSystemsDevelopment / qpdf

Give objects descriptions and context so it is possible to issue
warnings instead of fatal errors for attempts to access objects of the
wrong type.

Sometimes it's an offset in an object stream or a content stream, so
file position is confusing in some cases.

As in other cases, this is to enable adding new member variables in
the future without breaking ABI compatibility.

Expose Pl_QPDFTokenizer, and have it do more of the work of managing
the token filter's pipeline.

Implement a TokenFilter class and refactor Pl_QPDFTokenizer to use a
TokenFilter class called ContentNormalizer. Pl_QPDFTokenizer is now a
general filter that passes data through a TokenFilter.

Adding a trailing newline in content normalization damages files whose
contents are split across streams in the middle of tokens. Let
QPDFWriter add the newline with the indicator to ignore the newline,
which it already does. This changes the way some qdf files look.

Remove a redundant method that was equal to another one with
additional arguments. This breaks binary compatibility, but there are
other ABI breaking changes in the upcoming release, so now is the time
to do it.

This is for protection against future ABI breaking changes.

Significant enhancements to the lexer to improve EOF handling and to
support comments and spaces as tokens. Various other minor issues were
fixed as well.

This is useful only for debugging the linearization code.

Use 0 instead of NULL in a cast.

Different compilers want different choices of headers for std::abs.
It's easier to just to not use it.

Add options to enable the raw encryption key to be directly shown or
specified. Thanks to Didier Stevens <didier.stevens@gmail.com> for the
idea and contribution of one implementation of this idea.

Fix comment, remove restriction that doesn't actually matter.

If the stream isn't filterable but we call getStreamData, throw a
regular exception instead of a logic error so that normal error
handling and reporting mechanisms will be used.