Conveniently generating schema from a nested dict

I'm trying to use marshmallow to validate configuration files and I would like to know how to conveniently generate nested schemas using a dictionary.

Right now, this is the only method I could think of:

```python
def nest(obj):
return fields.Nested(Schema.from_dict(obj))

defaults = {
"path": nest(
{
"file": fields.Str(),
"more_file": fields.Str(),
}
),
"cred": nest(
{
"user": fields.Str(),
"pass": fields.Str(),
}
),
}

config = json.load(config_path)
schema = Schema.from_dict(defaults)()
schema.load(config)

```
But it's very inconvenient. Is there a better method that I'm not aware of?

Start with the Schema.from_dict and fields.Nested entry points shown in the example, and inspect how nested dictionaries are currently represented. Done means establishing a supported, more convenient way to generate nested schemas and confirming that it validates the configuration structure shown.

Written by the indexing model from the issue text.