Fix variable name in spawn function. Added working with json, upload examples and install&configuration documentation

doc/upload.rst

@@ -0,0 +1,20 @@
+Upload a file
+=============
+
+HTTP request allows us to send and receive files by using the Multipart standard.
+
+Kapow! allow us to handle files received in the request. In this example we
+respond back with the line count of the file received in the request.
+
+.. code-block:: bash
+
+  fname=$(kapow get /request/files/myfile/filename)
+  lcount=$(kapow get /request/files/myfile/content | wc -l)
+  kapow set /response/status 200
+  echo "$fname has $lcount lines" | kapow set /response/body
+
+You can try this by using the following curl:
+
+.. code-block:: bash
+
+  curl -F "myfile=@README.rst" http://localhost:8080/linecount