Added 2nd and 3th steps of tutorial

docs/source/tutorial/tutorial03.rst

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+What we've done?
+================
+
+**Senior**
+
+  Hi guy!  How're you doing this morning?  I've got a new challenge from our
+  grateful mates.
+
+  As time goes on from the last rotation the size of the log file gets bigger.
+  Furthermore, they want to limit the output of the file to pick only some
+  records and only from the end of the file.  We need to do something to help
+  them as they waste a lot of time reviewing the output.
+
+**Junior**
+
+  My two cents is that this time is going to be more of a deep bash knowledge.
+  Do you agree?
+
+**Senior**
+
+  By sure, but in addition to some good shell plumbing we're going to squeeze
+  Kapow!'s superpowers a litle bit more to get a really good solution.
+
+  Can you take a look at Kapow!'s documentation to see if something can be done?
+
+**Junior**
+
+  I've seen in the documentation and there is a way to get access to the data
+  comming in the request.  Do you think we can use this to let them choose how
+  to do the filtering?
+
+**Senior**
+
+  Sounds great!  How could we live without Kapow! all this time?
+
+  As they requested, we can offer them with a parameter to filter the registers
+  they want to pick and another parameter to limit the output size in lines.
+
+**Junior**
+
+  Sounds that will be enough.  Now we have to make some modifications to our
+  last endpoint definition to add this new feature.  Let's start working...
+
+**Senior**
+
+  Well, we got it again, this is exactly what they need:
+
+  .. code-block:: sh
+
+     kapow route add /db/backup_logs -e grep "$(kapow get /request/params/filter)" /var/log/backup_db.log \
+       | tail -n "$(kapow get /request/params/lines)" \
+       | kapow set /response/body
+
+  It looks a bit weird but we'll have time to re-styling later.  Please make
+  some tests on your laptop before to publish on the *Corporate Server*.
+  Remember to send them an example URL with the parameters the can use to
+  filter.
+
+**Junior**
+
+  Ok, Should look like this, isn't it?
+
+  .. code-block:: console
+
+     $ curl http://localhost:8080/db/backup_logs?filter=rows%20inserted&lines=200
+
+**Senior**
+
+  Exactly.  Another great day helping the company to advance.  Let's go for a
+  beer for celebrating!