OpenSystemsDevelopment / qpdf

Prior to this fix, if there was a loop detected in following /Prev
pointers in xref streams/tables, it would cause qpdf to lose data.
Note that this condition causes many PDF readers to hang or fail.

This is for testing the release process, particularly as it pertains
to AppImage creation.

Bump to an alpha release. This version is not being widely released
but is being used to push the new shared library version through the
debian packaging system and to test out github releases.

The QPDF_String::getUTF8Val() method was not treating strings that
weren't explicitly Unicode as PDF Doc Encoded. This only affects
characters in the range 0x80 through 0xa0.

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.