Add a * select to match all changes. Fixes #23.

This pull request adds a `*` context that acts as a catch all.

```js
var queries = [
    {
        context: 'mobile',
        match: function() {
            console.log('Mobile callback. Maybe hook up some tel: numbers?');
        },
        unmatch: function() {
            // We're leaving mobile.    
        }
    },
    {
        context: '*',
        match: function() {
            console.log('Changed breakpoint.');
        }
    }
];
// Go!
MQ.init(queries);
</script>
```

Now `Changed breakpoint.` will **also** be logged to the console any time any break point is matched.