Fixed a bug (on my machine) and added a option to bind to different address

* Added an option -o (copied this from sinatra) to select different different address to  bind as the default address is localhost

* The gem was not working on my machine with the error no method ```send``` .
I have to add the following code to make it work 

```
Sinatra::Base.send request_mapping.method, request_mapping.path, &block
```

Let me know If I am missing anything