Windows nightly builds now bundle dependencies into OpenSlide DLL

[Benjamin Gilbert]

Hi all,

Beginning with tonight's nightly build, the OpenSlide Windows binaries
bundle most dependencies directly in the OpenSlide DLL, rather than
shipping them as separate DLL files.  (There are currently two
exceptions, winpthreads and libssp, which we may be able to address
later.)  This arrangement should avoid symbol conflicts between
OpenSlide's dependencies and other builds of the same libraries, e.g.
conflicts with zlib or libjpeg when using OpenSlide in Anaconda.

Please test the build and report any issues:

    https://github.com/openslide/builds/releases/tag/windows-20230326-nightly

If I don't hear of any problems, I'm planning to release a new stable
build with these changes in the next couple weeks.

--Benjamin Gilbert