loads() returns inconsistent types

[medwig]

python -c "import geojson; geojson.loads('{}').is_valid"
AttributeError: 'dict' object has no attribute 'is_valid'

If loads(x) succeeds it returns a geojson.feature.____ object, otherwise it returns the result of json.loads(x).

I recommend it always return a feature object.

[frewsxcv]

Sounds good to me, though we'll need to do a major version bump for this, which is fine