Update networking layer w/ CURL and emscripten impl

External/curl-8.17.0/docs/libcurl/curl_mime_addpart.md

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+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: curl_mime_addpart
+Section: 3
+Source: libcurl
+See-also:
+  - curl_mime_data (3)
+  - curl_mime_data_cb (3)
+  - curl_mime_encoder (3)
+  - curl_mime_filedata (3)
+  - curl_mime_filename (3)
+  - curl_mime_headers (3)
+  - curl_mime_init (3)
+  - curl_mime_name (3)
+  - curl_mime_subparts (3)
+  - curl_mime_type (3)
+Protocol:
+  - HTTP
+  - IMAP
+  - SMTP
+Added-in: 7.56.0
+---
+
+# NAME
+
+curl_mime_addpart - append a new empty part to a mime structure
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+curl_mimepart *curl_mime_addpart(curl_mime *mime);
+~~~
+
+# DESCRIPTION
+
+curl_mime_addpart(3) creates and appends a new empty part to the given
+mime structure and returns a handle to it. The returned part handle can
+subsequently be populated using functions from the mime API.
+
+*mime* is the handle of the mime structure in which the new part must be
+appended.
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+int main(void)
+{
+  curl_mime *mime;
+  curl_mimepart *part;
+
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    /* create a mime handle */
+    mime = curl_mime_init(curl);
+
+    /* add a part */
+    part = curl_mime_addpart(mime);
+
+    /* continue and set name + data to the part */
+    curl_mime_data(part, "This is the field data", CURL_ZERO_TERMINATED);
+    curl_mime_name(part, "data");
+  }
+}
+~~~
+
+# %AVAILABILITY%
+
+# RETURN VALUE
+
+A mime part structure handle, or NULL upon failure.