Update networking layer w/ CURL and emscripten impl

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

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+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_APPEND
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_DIRLISTONLY (3)
+  - CURLOPT_RESUME_FROM (3)
+  - CURLOPT_UPLOAD (3)
+Protocol:
+  - FTP
+  - SFTP
+Added-in: 7.17.0
+---
+
+# NAME
+
+CURLOPT_APPEND - append to the remote file
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_APPEND, long append);
+~~~
+
+# DESCRIPTION
+
+A long parameter set to 1 tells the library to append to the remote file
+instead of overwrite it. This is only useful when uploading to an FTP site.
+
+# DEFAULT
+
+0 (disabled)
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+
+    curl_easy_setopt(curl, CURLOPT_URL, "ftp://example.com/dir/to/newfile");
+    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
+    curl_easy_setopt(curl, CURLOPT_APPEND, 1L);
+
+    curl_easy_perform(curl);
+  }
+}
+~~~
+
+# HISTORY
+
+This option was known as CURLOPT_FTPAPPEND up to 7.16.4
+
+# %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).