OpenSystemsDevelopment / qpdf

Change "-" to "--" for named parameters.
Remove spaces inside "[ option ]" for optional parameters.
Fix "pdf-mod-info --dump file" to match usage message.

None of these are in the public API.

Let argv be a null-terminated array. There is already code that
assumes this, and it makes it easier to construct the arguments.

Use QPDFObjectHandle::isNameAndEquals, isDictionaryOfType and
isStreamOfType.

The /Subtype entry that specifies the mime type of an embedded file is
inside the embedded file stream dictionary directly, not it in the
parameter dictionary.

See Table 45 and 46 in the PDF 1.7 specification:
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#page=112

Use the first of ASCII, PDFDocEncoding, or UTF-16 that is capable of
encoding the string.

A class can't have a PointerHolder to itself since PointerHolder
doesn't have the concept of weak references.

This change works around STL problems with Embarcadero C++ Builder
version 10.2, but std::vector is more common than std::list in qpdf,
and this is a relatively new API, so an API change is tolerable.

Thanks to Thorsten Schöning <6223655+ams-tschoening@users.noreply.github.com>
for the fix.