Do not ignore single bikes outside a station
https://github.com/eskerda/pybikes/blob/032f47ae8427468a2cf2babfbcf100ce473e320c/pybikes/nextbike.py#L57 In some cities, such as Dresden, almost all bikes are "roaming around" and there are few stations or none at all. Ignoring these bikes will render pybikes useless for those cities. Nevertheless, it probably does not make sense to list them under "stations", maybe there needs to be a new attribute?
Also: sorting out if bikes=1 also sorts out real stations that happen to have only 1 bike present, right?
The correct way seems to be via the attribute spot="1" which seems to be only present for stations but not for single roaming bikes.
Fixed by #417 (even though the pull request does a lot more)