Added jasmine.async.d.ts TypeScript definition file

This definition file allows the use of this with TypeScript.

For example:  
```typescript
var async: asyncjasmine.AsyncSpec = new asyncjasmine.AsyncSpec(this);

async.beforeEach((done) => {
    //to stuff
    done();
});

async.it('is awesome', (done) => {
    setTimeout(() => {
        expect(true).toBe(true);
        done();
    }, 500);        
});

async.afterEach((done) => {
    //to stuff
    done();
});

```