Python 3 fixes (fixes #129)

Hey. To get this library working under python 3, I had to make some small changes. 

Note that I'm not quite sure about the change to recvall, should this return bytes or a string? Also, it might be more pythonic and faster to generate a list of items, then join them together. 

If I get some comments about this, I could also try to add some unit tests if needed.

For reference, my code was something along the lines of:

```python
c = docker.Client()
container = client.create_container(
    "something", 
    command=['ls', '/'],
    volumes={'/code':{}}
)

c.start(container, binds={'~': '/code'})
for line in c.logs(container, stream=True):
    print(line.decode("utf-8"),)
```