Add some examples

Note that the example on redirecting a URL is BROKEN.  Possibly a bug in Kapow!

doc/reading_headers.rst

@@ -0,0 +1,13 @@
+Reading Headers
+===============
+
+The HTTP protocol allows metadata using headers.
+
+Kapow! allows you to read them easily:
+
+
+In this example, we read the header ``User-Agent`` and feed it
+to the response:
+.. code-block:: bash
+
+   kapow get /request/headers/User-Agent | kapow set /response/body

doc/redirecting_a_url-BROKEN.rst

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+Redirecting a URL
+=================
+
+The HTTP protocol allows queries to a URL to be redirected to other URL.
+
+We can do them in Kapow! with little effort:
+
+In this example, we read the header ``User-Agent`` and feed it to the response:
+.. code-block:: bash
+
+   echo -n 302 | kapow set /response/status
+   echo -n http://foobar-url.example | kapow set /response/headers/Location

doc/writing_headers.rst

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+Writing Headers
+===============
+
+The HTTP protocol allows metadata using headers.
+
+Kapow! allows you to set them easily:
+
+
+In this example, we respond by setting the ``Content-Type`` header
+to the value ``application/json``.
+.. code-block:: bash
+
+   kapow set /response/headers/Content-Type application/json
+
+We could then return some JSON content:
+.. code-block:: bash
+
+   echo '{"data": "some relevant string"}' | kapow set /response/body