Add an example showing the new form API.

examples/README

@@ -1,6 +1,6 @@
 add_header.py           Simple script that just adds a header to every request.
 flowbasic               Basic use of mitmproxy as a library.
+modify_form.py          Modify all form submissions to add a parameter. 
 stub.py                 Script stub with a method definition for every event. 
 stickycookies           An example of writing a custom proxy with libmproxy.
 upsidedownternet.py     Rewrites traffic to turn PNGs upside down.
-

examples/modify_form.py

@@ -0,0 +1,8 @@
+
+def request(context, flow):
+    if "application/x-www-form-urlencoded" in flow.request.headers["content-type"]:
+        frm = flow.request.get_form_urlencoded()
+        frm["mitmproxy"] = ["rocks"]
+        flow.request.set_form_urlencoded(frm)
+
+