Feature request: 'interfacePrefix'

Hi! First of all thanks for this project!

Currently, there are several props for prefix\suffix settings:

```
typePrefix: '',
typeSuffix: '',
enumKeyPrefix: '',
enumKeySuffix: '',
```

But the one is missing is `interfacePrefix` (and `interfaceSuffix`).

Ideally, I want to have a `"T"` prefix for my types, and `"I"` for my interfaces, as far as I understand, currently it's impossible, and `typePrefix` will be applied to both types and interfaces.

Thanks!