Programmatically change title of test case

Right now it has to be done by using [this hack](https://coderwall.com/p/riklkg)

Provide a `this.title()` method inside a test case such that it returns the present test case's title if called without any argument. If called with an argument set it as the title of that test case. 

### Use Case
So that we can do something like this. Displaying the input along with the title in report.
```javascript
var assert = require('assert');

describe("My Test", function(){
    it("should pass with input ", function(){
        var input = "This will be appended at the end of the title ";
        this.title( this.title() + input );
        assert(typeof input === 'string');
    });
});
```