How to use D without the GC ?

[bachmeier]

A SafeRefCounted example with main marked @nogc:

```
import std;
import core.stdc.stdlib;

struct Foo {
   double[] data;
   double * ptr;
   alias data this;

   @nogc this(int n) {
     ptr = cast(double*) malloc(n*double.sizeof);
     data = ptr[0..n];
     printf("Data has been allocated\n");
   }

   @nogc ~this() {
     free(ptr);
     printf("Data has been freed\n");
   }
}

@nogc void main() {
   auto foo = SafeRefCounted!Foo(3);
   foo[0..3] = 1.5;
   printf("%f %f %f\n", foo[0], foo[1], foo[2]);
}
```