SIP: Structural Types

The following changes were suggested at the SIP meeting:

Instead of `selectDynamicMethod`, use `applyDynamic` and pass the arguments directly in a separate list:
```
def selectDynamicMethod(name: String, paramClasses: ClassTag[_]*): Any
```
becomes
```
def applyDynamic(name: String, paramClasses: ClassTag[_]*)(args: Any*): Any
```

