Adding a function to be able to compare lime.fill.Color

Initially I was doing this

```javascript
var color1 = new lime.fill.Color([10, 10, 12]);
var color2 = new lime.fill.Color([10, 10, 100);
if (color1.str ==  color2.str) console.log('yay');
```
but I occasionally I kept forgetting to compare the `.str` and was doing `color1 === color2` which doesnt work. 

With this commit I can do the following which is a bit more explicit

```javascript
if (color1.equals(color2)) console.log('yay');
```