JsonSchemaGenerator doesn't support StringEnumConverter

When using `JsonSchemaGenerator` to `Generate` a schema for a type with a property decorated with `StringEnumConverter`, the generated schema contains integer and not string values for the enum:
```json
{
	"enum": [
		0,
		1,
		2,
		3,
		4
	]
}
```
It would be neat if the generated schema took the `StringEnumConverter` into consideration. It would also be neat if the generated schema (and serialized JSON) could enforce all-lowercase string values for the enum. There seems to have been [done some work on this over at CodePlex](https://json.codeplex.com/discussions/245604), but it's rather old so I'm not sure how relevant that is anymore.