Fixing entities

1) thanks for verbosity hint
2) asked sat6 devs, most of the names are char[255], meaning, that if using utf, that has wider characters, generated names needs to be much smaller, so changing to 100

How about a pair of `setdefault` statements? if the user has explicitly set a content-type, we shouldn't overwrite that. Something like this:

```python
kwargs.setdefault('data', {})
kwargs['headers'].setdefault('Content-Type', 'application/json')
```