First Draft: Tuple Unpacking Syntax

[Walter Bright]

This is a well written DIP. Congratulations!

The forward range tuple is pretty cool.

Let's move forward with this.

bearophile's example uses `_` as a placeholder, but I don't see it mentioned in 
the rest of the DIP?

For the example:
```
auto arr = [tuple(1, "2"), tuple(3, "4"), tuple(5, "6")];

foreach((x, y); arr) {
     writeln(x, " ", y); // "1 2\n3 4\n5 6"
}

foreach((int x, string y); arr) {
     writeln(x, " ", y);// "1 2\n3 4\n5 6"
}
```

shouldn't there be a trailing \n after the 6?