Update networking layer w/ CURL and emscripten impl

External/curl-8.17.0/docs/libcurl/opts/CURLOPT_TRAILERDATA.md

@@ -0,0 +1,61 @@
+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_TRAILERDATA
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_TRAILERFUNCTION (3)
+  - CURLOPT_WRITEFUNCTION (3)
+Protocol:
+  - HTTP
+Added-in: 7.64.0
+---
+
+# NAME
+
+CURLOPT_TRAILERDATA - pointer passed to trailing headers callback
+
+# SYNOPSIS
+
+~~~c
+#include <curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERDATA, void *userdata);
+~~~
+
+# DESCRIPTION
+
+Data pointer to be passed to the HTTP trailer callback function.
+
+# DEFAULT
+
+NULL
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+struct MyData {
+  void *custom;
+};
+
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    struct MyData data;
+    curl_easy_setopt(curl, CURLOPT_TRAILERDATA, &data);
+  }
+}
+~~~
+
+# %AVAILABILITY%
+
+# RETURN VALUE
+
+curl_easy_setopt(3) returns a CURLcode indicating success or error.
+
+CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
+libcurl-errors(3).