objc_class

Given

```
newtype MyObjCClass = MyObjCClass (ForeignPtr MyObjCClass)
```

`objc_class ''MyObjCClass` should generate

```
objc_interface [cunit| @class MyObjCClass; |]
myObjClass :: MyObjCClass -> IO MyObjCClass
myObjClass = return
objc_marshaller 'myObjClass 'myObjClass
```
