HTTP connection pooling
A customer has reported that when doing this they get expected reuse of the HTTP connection pooling:

```python
client = AblyRest('api:key')
channel = client.channels.get('channel_name')
channel.publish('foo', 'bar')
# Slower request expected as new TCP TLS connection needed 
channel.publish('foo', 'bar')
# Faster as previous connection reused automatically
```

However, when they do this, they don't get HTTP connection reuse:

```python
client = AblyRest('api:key')
channel = client.channels.get('channel_name')
channel.publish('foo', 'bar')
# Slower request expected as new TCP TLS connection needed 
client2 = AblyRest('api:key')
channel2 = client2.channels.get('channel_name')
channel2.publish('foo', 'bar')
# Equally slow request as first
```

In other libraries, the underlying HTTP library automatically handles connection reuse so long as the requests are in the same process, whereas with Python it seems this is not the case and the pooling is only done with the instance REST client.

This is not the intended behaviour.
diff --git a/ably/http/http.py b/ably/http/http.py
index 8f077e5..a01e693 100644
--- a/ably/http/http.py
+++ b/ably/http/http.py
@@ -105,12 +105,13 @@ class Http(object):
         'http_max_retry_duration': 15,
     }
 
+    __session = requests.Session()
+
     def __init__(self, ably, options):
         options = options or {}
         self.__ably = ably
         self.__options = options
 
-        self.__session = requests.Session()
         self.__auth = None
 
     def dump_body(self, body):
diff --git a/ably/rest/rest.py b/ably/rest/rest.py
index c6749f3..2068564 100644
--- a/ably/rest/rest.py
+++ b/ably/rest/rest.py
@@ -64,11 +64,6 @@ class AblyRest(object):
         else:
             options = Options(**kwargs)
 
-        # if self.__keep_alive:
-        #     self.__session = requests.Session()
-        # else:
-        #     self.__session = None
-
         self.__http = Http(self, options)
         self.__auth = Auth(self, options)
         self.__http.auth = self.__auth
['ably/http/http.py', 'ably/rest/rest.py']