Make mg_http_check_digest_auth() public

PUBLISHED_FROM=f00b94cabc2a89d27d5bc78d68d67db0930811b4

docs/c-api/http.h/items.json

@@ -104,6 +104,10 @@
             "type": "markdown",
             "name": "mg_file_upload_handler.md"
         },
+        {
+            "type": "markdown",
+            "name": "mg_http_check_digest_auth.md"
+        },
         {
             "type": "markdown",
             "name": "mg_fu_fname_fn.md"