Parameterizable type aliases

Please make type aliases parameterizable, just like structs and functions. For example, this would be nice:

`type MyArray = u8[Num];`

Today this is a `ParseError`.

Furthermore, let's make sure that parameters are 'forwarded' properly, such as in this example:

```
type Frob = uN[Cats];
type Widget = Frob[Dogs];
```