Add two more examples: dup_and_replay.py and modify_querystring.py

examples/README

@@ -1,6 +1,8 @@
 add_header.py           Simple script that just adds a header to every request.
+dup_and_replay.py       Duplicates each request, changes it, and then replays the modified request.
 flowbasic               Basic use of mitmproxy as a library.
 modify_form.py          Modify all form submissions to add a parameter. 
+modify_querystring.py   Modify all query strings to add a parameters.
 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/dup_and_replay.py

@@ -0,0 +1,4 @@
+def request(ctx, flow):
+   f = ctx.duplicate_flow(flow)
+   f.request.path = "/changed"
+   ctx.replay_request(f)

examples/modify_querystring.py

@@ -0,0 +1,7 @@
+
+def request(context, flow):
+    q = flow.request.get_query()
+    if q:
+        q["mitmproxy"] = ["rocks"]
+        flow.request.set_query(q)
+