[DO-976] libpng recipe (!5)

Co-authored-by: aleksandr.vodyanov <aleksandr.vodyanov@avroid.tech>
Reviewed-on: https://git.avroid.tech/Conan/conan_build/pulls/5

recipes/libpng/all/test_package/test_package.c

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include "png.h"
+
+
+int main(void) {
+    png_structp png_ptr;
+    png_infop info_ptr;
+
+    fprintf(stderr, "   Compiled with libpng %s; using libpng %s.\n", PNG_LIBPNG_VER_STRING, png_libpng_ver);
+    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
+    info_ptr = png_create_info_struct(png_ptr);
+
+    return EXIT_SUCCESS;
+}