Documentation generator is not working

[Vinod K Chandran]

Hi all,
I am playing with ddoc. I wrote this code--
```d
import std.stdio : log = writeln;

void main() {
     log("Experimenting with dDoc");
}

/// A sample function.
/// Let's check what we will get in documentation.
/// abc - A simple string
void sample(string abc) {log(abc);}
```
And then, compile it with "-D" switch. At first, I saw an html 
file is generated. But I deleted it and compiled again. This 
time, no html file is generated. What's wrong with this ?