docs and macro fix

docs/mithril.request.md

@@ -10,6 +10,7 @@
 - [Casting the Response Data to a Class](#casting-the-response-data-to-a-class)
 - [Unwrapping Response Data](#unwrapping-response-data)
 - [Using Different Data Transfer Formats](#using-different-data-transfer-formats)
+- [File uploads with FormData](#file-uploads-with-form-data)
 - [Using variable data formats](#using-variable-data-formats)
 - [Extracting Metadata from the Response](#extracting-metadata-from-the-response)
 - [Custom request rejections](#custom-request-rejections)
@@ -252,6 +253,26 @@ var file = m.request({
 
 ---
 
+### File uploads with FormData
+
+To use the HTML5 FormData object as the payload for a request, you need to override the `serialize` option. By default, `serialize` converts an object to JSON, but in the case of a FormData payload, you want to pass the object intact.
+
+```javascript
+//assume the file comes from an HTML5 drag-n-drop event
+var file = e.dataTransfer.files[0]
+
+var data = new FormData();
+data.append("file", file)
+
+m.request({
+	method: "POST",
+	url: "/upload",
+	serialize: function(data) {return data}
+})
+```
+
+---
+
 ### Using variable data formats
 
 By default, Mithril assumes both success and error responses are in JSON format, but some servers may not return JSON responses when returning HTTP error codes (e.g. 404)