api: Introduce the `PNG_LIBPNG_VER_SHAREDLIB` macro; update pngwin.rc
The version macros `PNG_LIBPNG_VER_SONUM` and `PNG_LIBPNG_VER_DLLNUM`
weren't always in sync, but they should be, going forward.
Or, better yet, we should keep them in, deprecated, and introduce
`PNG_LIBPNG_VER_SHAREDLIB` for all shared library builds of all kinds
on all platforms.
It is unknown how many user applications have been using these macros.
We have been using `PNG_LIBPNG_VER_DLLNUM` for pngwin.rc, for example.
Which, by the way, was last updated in 2009.
3 files changed
