OpenSystemsDevelopment / qpdf

Now that the test suite runs clean with address sanitizer, add some
test cases that previously were used to expose memory errors.

There was a missing free causing a memory leak in some test code. The
memory leak was not in library code.

Resolve link error on cygwin

Most of the README files have been renamed. Refer to the new names.

Slightly improve memory cleanup in Pl_DCT
Make it easier to test with valgrind

While scanning the file looking for objects, limit the length of
tokens we allow. This prevents us from getting caught up in reading a
file character by character while digging through large streams.

A stray semicolon caused a condition to be incorrectly applied during
stream length recovery.

Pushing member variables into a nested class enables addition of new
member variables without breaking binary compatibility.

Reduce code duplication

Files written in PCLm mode have to be created in a very specific way.
qpdf doesn't know how to create PCLm files from scratch. All it knows
how to do is to write an already valid file in a suitable way.
Therefore there is no command-line support for PCLm.

Remove duplicated coverage cases from Sahil's code so existing test
suite passes.

* Add support for PCLm using setPCLm() and writePCLm() methods in
  QPDFWriter.hh and QPDFWriter.cc
* Add a function writePCLmHeader() for PCLm header in QPDFWriter

Replace the old msys, mingw-w64, ActiveState perl setup with MSYS2.
This greatly simplifies the Windows build. This was facilitated by the
need to incorporate JPEG.