add "har" as official (enough) grammar

[monkyyy]

dlang.io does the `--- foo.d` to mean "the stuff under this is 
part is foo.d"

this is like `#!` in that it allows for terse things to happen 
automagicly but the compiler needs to know to ignore it with a 
fairly lazy hack

```d
import std;
--- hello.d

void main(){
   "hello".writeln;
}
```

Should have a warning: "line 2 `har` detected, did you mean to 
use a different tool for this?" but then compile ignoring it. 
Then like `#!` drastically improves dlangs scriptablity from a 
level of compatibility that would be basically impossible to 
implement