Add streaming_how_to.rst. A high level tutorial for getting started with streaming.

docs/streaming_how_to.rst

+.. _streaming_how_to:
+.. _Twitter Streaming API Documentation: https://dev.twitter.com/streaming/overview
+
+*********************
+Streaming With Tweepy
+*********************
+Tweepy makes it easier to use the twitter streaming api by handling authentication, 
+connection, creating and destroying the session, reading incoming messages, 
+and partially routing messages. 
+
+This page aims to help you get started using Twitter streams with Tweepy 
+by offering a first walk through. 
+
+API authorization is required to access Twitter streams. 
+Follow the :ref:`auth_tutorial` if you need help with authentication. 
+
+Summary
+=======
+The Twitter streaming API is used to download twitter messages in real 
+time.  It is useful for obtaining a high volume of tweets, or for 
+creating a live feed using a site stream or user stream. 
+See the `Twitter Streaming API Documentation`_.
+
+The streaming api is quite different from the REST api because the
+REST api is used to *pull* data from twitter but the streaming api
+*pushes* messages to a persistent session. This allows the streaming 
+api to download more data in real time than could be done using the
+REST API. 
+
+In Tweepy, an instance of **tweepy.Stream** establishes a streaming 
+session and routes messages to **StreamListener** instance.  The
+**on_data** method of a stream listener receives all messages and
+calls functions according to the message type. The default 
+**StreamListener** can classify most common twitter messages and 
+routes them to appropriately named methods, but these methods are 
+only stubs. 
+
+Therefore using the streaming api has three steps. 
+
+1. Create a class inheriting from **StreamListener**
+
+2. Using that class create a **Stream** object 
+
+3. Connect to the Twitter API using the **Stream**.
+
+
+Step 1: Creating a **StreamListener**
+=====================================
+This simple stream listener prints status text.
+The **on_data** method of Tweepy's **StreamListener** conveniently passes 
+data from statuses to the **on_status** method.
+Create class **MyStreamListener** inheriting from  **StreamListener** 
+and overriding **on_status**.::
+  import tweepy
+  #override tweepy.StreamListener to add logic to on_status
+  class MyStreamListener(tweepy.StreamListener):
+  
+      def on_status(self, status):
+          print(status.text)
+
+Step 2: Creating a **Stream**
+=============================
+We need an api to stream. See :ref:`auth_tutorial` to learn how to get an api object. 
+Once we have an api and a status listener we can create our stream object.::
+
+  myStreamListener = MyStreamListener()
+  myStream = tweepy.Stream(auth = api.auth, listener=myStreamListener())
+
+Step 3: Starting a Stream
+=========================
+A number of twitter streams are available through Tweepy. Most cases 
+will use filter, the user_stream, or the sitestream. 
+For more information on the capabilities and limitations of the different
+streams see `Twitter Streaming API Documentation`_.
+
+In this example we will use **filter** to stream all tweets containing
+the word *python*. The **track** parameter is an array of search terms to stream. ::
+  
+  myStream.filter(track=['python'])
+
+
+
+