viz.create_html() rounds lat/lng to 4 decimal places which drops accuracy to 11m

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This is the difference between this:

And this:

This is happening here:
https://github.com/mapbox/mapboxgl-jupyter/blob/9a15a0759db5b0c5dc8d59f4a8e0d77b9c378daf/mapboxgl/viz.py#L281

I'm attempting to solve this by passing in a decimal rather than a float when building my FeatureCollection:
```
features.append(Feature(
geometry=Point((Decimal(m['lng']), Decimal(m['lat']))),
))
```

You can monkey patch this like this:

```
import json
import decimal

class FullJSONEncoder(json.JSONEncoder):
def default(self, o):
if isinstance(o, decimal.Decimal):
return str(o)
return super().default(o)

default_props = {'cls': FullJSONEncoder, 'skipkeys': False, 'check_circular': False, 'allow_nan': False, 'indent': False, 'separators': None, 'default': None, 'sort_keys': False, 'ensure_ascii': False}
with patch.object(json.dumps, '__kwdefaults__', default_props):
...
```

Start at mapboxgl/viz.py around line 281, where viz.create_html() handles the coordinate data, and reproduce the reported precision loss with the Decimal-based FeatureCollection example. Done means generated HTML preserves the latitude and longitude accuracy instead of rounding them to four decimal places.

Written by the indexing model from the issue text.