[#706] PEP8 Compliance

If you want me to actually remove the changes from `dht.py`, `market.py` and `transport.py` let me know.
I can also add a test for PEP8 compliance.
Sounds good. According to pep257 it should be something more like this:

```python
"""Enum inner class.

Python introduces enums in Python 3.0, but this should be good enough.

"""
```

But I don't see any that follow that format so I will go with
```python
"""
Enum inner class. 

Python introduces enums in Python 3.0, but this should be good enough.
"""
```