OpenSystemsDevelopment / qpdf

Fix typo in --rotate example

Don't assume endobj is at the beginning of the line. This means we are
looking at tokens for every line, but the odds of n n obj appearing in
the middle of the object are likely much lower than endobj not being
at the beginning of the line or missing entirely. This will probably
have a negative impact on recovery time for very large files.
Hopefully it will be worth it.

Main branch is `main` now

Thanks @neuhaus!

When making resources indirect in from_dr, the code was using the
wrong owning QPDF, forgetting that from_dr had already been copied
using CopyForeignObject.

When adding a QPDFObjectHandle to an array or dictionary, if possible,
check if the new object belongs to the same QPDF. This makes it much
easier to find incorrect code than waiting for the situation to be
detected when the file is written.

This was originally not public because I wanted to get rid fo the
pages cache, but I recently realized there were deep reasons not to do
that, and the author of pikepdf wanted this, so I decided to make it
public.

Also switch URLs for the qpdf and qtest websites to sourceforge.io
(https) instead of sourceforge.net (http).

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

Add a new make target that installs the qpdf libraries without
executables or documentation.

This solves
  libtool: compile: unable to infer tagged configuration
  libtool:   error: specify a tag with '--tag'
build issues when using toolchain that prevents libtools
inference rules from working correctly (e.g. ccache).

Check for this->encrypt seems to be moved to plugged crypto
implementations, so it can be removed from Pl_AES_PDF.cc.