Relationship support for Models

Usage : 

    php artisan generate:model Baby --relationships="has_many:foo, has_one:buzz"

This will create 

```
<?php

class Baby extends Eloquent {

    public function foo() 
    {
        return $this->has_many('Foo');
    }
    public function buzz()
    {
        return $this->has_one('Buzz');
    }

}
```