Update city_schema.json

[hbruch]

This PR fixes #219 by updating city_schema.json.

Note that nevertheless, some current city responses are not valid according to this schema.

Especially Aarhus and Koeln currently report states as "unknown", which IMHO should be reported as "nodata". Further, Koeln reports free=-1 for some parkings. As this seems to represent an unknown value. If true, it should rather be left out, as it is not mandatory.

Note further, that this schema uses some anyOf-type-validations, to allow currently used practice to specify null values for values required by the former schema, but apparently unknown. IMHO null should not be allowed for required properties, but that would result in rework for some data providers.

Finally, this schema s rather strict by not allowing additionalProperties. This kind of blocks experimental features, but uncovers properties not yet specified in the schema. Probably, additionalProperties should better be set to true.

[hbruch]

Looks like the latest feedparser makes use of python 3.6 string formatting syntax (f'), which fails the build. I guess that either feedparser version should be frozen at an earlier version in requirements.txt or minimum compatibility raised to 3.6.

[jklmnn]

Looks like the latest feedparser makes use of python 3.6 string formatting syntax (f'), which fails the build. I guess that either feedparser version should be frozen at an earlier version in requirements.txt or minimum compatibility raised to 3.6.

Thanks for looking at this issue. I think we can safely drop Python 3.5 since even Debian Stable (which we use) has already Python 3.7. (see #222). Do you have any requirement in this regard? If you need Python 3.6 I would still include it otherwise I'd make Python 3.7 the minimum version.

[hbruch]

No objections to moving to python 3.7 as minimum requirement. I'll open an issue to gather what needs to be done.

[hbruch]

I resolved the state related change requests, switched additonalProperties to true, to allow custom extensions and updated the README.md example to reflect the schema.

[jklmnn]

Fixed by 3f2eb37.