that CCP writes to standard output by default (Martin Banky).

  The changes include support for function attributes in VC in addition to
    those already present in GCC - necessary because without these some
    warnings are unavoidable.  Fixes include signed/unsigned fixes in
    pngvalid and checks with gcc -Wall -Wextra -Wunused.
  VC requires function attributes on function definitions as well as
    declarations, PNG_FUNCTION has been added to enable this and the
    relevant function definitions changed.

that were recently introduced, mostly resulting from
safe but uncast assignments to shorter integers.  Also added a zlib
VStudio release library project because the latest zlib Official Windows
build does not include such a thing.