dub -debug=tag for Windows

[Brother Bill]

Page 462 of Programming in D book.

The goal is to only run debug(binarySearch), and not regular 
debug.
Looking for the CLI for dub or dmd.
Tried:
> dmd source/app.d -w -debug=binarySearch
but it printed all the debug statements.

What CLI command will get the job done?

```
import std.stdio;

void main() {
     auto numbers = [-100, 0, 1, 2, 7, 10, 42, 365, 1000];
     auto index = binarySearch(numbers, 42);

     writeln("Index: ", index);
}

size_t binarySearch(const int[] values, int value) {
     debug writefln("searching %s among %s", value, values);

     if (values.length == 0) {
         debug(binarySearch) writefln("%s not found", value);
         return size_t.max;
     }

     immutable midPoint = values.length / 2;

     debug writefln("considering index %s", midPoint);

     if (value == values[midPoint]) {
         debug writefln("found %s at index %s", value, midPoint);
         return midPoint;

     } else if (value < values[midPoint]) {
         debug(binarySearch) writefln("must be in the first half");
         return binarySearch(values[0 .. midPoint], value);

     } else {
         debug writefln("must be in the second half");
         return binarySearch(values[midPoint + 1 .. $], value);
     }
}

```