OpenSystemsDevelopment / qpdf

Updated instructions for setting LD_LIBRARY_PATH to suggest modifying .bashrc.

Added information about setting LD_LIBRARY_PATH for installation.

* Based on feedback, keep gpg as well as cosign for the indefinite
  future
* Streamline release creation process by using the `gh` command-line
  tool (GitHub's official CLI) rather than old-school curl directly
  against the GitHub API, a procedure that predates the `gh` command.

This requires a special build option.

Use "QPDF" only for the QPDF class itself.

For now, we are using codecov as an internal tool and not advertising
code coverage. I scrutinize coverage on include and libqpdf but don't
want to remove coverage reporting for other areas.

Over time, qpdf's grade has dropped on lgtm, but they are not
transparent about how grades are assigned. Fixing current alerts, in
my opinion, reduces clarity and maintainability of the code in the
name of performance in non-critical sections of code. Some analysis by
m-holger suggests that fixing some of the current alerts actually
degrades performance (slightly) while fixing others results in
insignificant improvements. The quality of qpdf can be measured in
other ways, such as its extensive test suite, documentation, and long
track record of reliably manipulating PDFs with high performance, few
bugs, and few external dependencies. The lgtm rating is a distraction
at best.

Some people don't know what CI is, so remove use of that abbreviation
when it doesn't add any value.

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

External libraries for Windows are now built automatically in the
qpdf/external-libs repository and include openssl in addition to zlib
and jpeg. Use these, and update the Windows build to build with the
openssl crypto provider by default. We leave the native crypto
provider enabled in case there is a problem with openssl and also to
continue to exercise that code.

It is redundant with qpdf's main CI environment, which is Azure
Pipelines, but may soon be migrated to GitHub Actions.