Added a way to modify default options globaly

Added a simple way to modify default options globaly, a few example :
*French Translation:*
```javascript
$.fn.magicSuggest.defaults = $.extend({}, $.fn.magicSuggest.defaults, {
    maxEntryRenderer: function(v) {
        return 'Tag trop long de ' + v + ' caractère' + (v > 1 ? 's':'');
    },
    maxSelectionRenderer: function(v) {
        return 'Vous ne pouvez pas choisir plus de ' + v + ' tag' + (v > 1 ? 's':'');
    },
    minCharsRenderer: function (v) {
        return 'Merci de saisir ' + v + ' caractère' + (v > 1 ? 's' : '') + ' de plus';
    },
    noSuggestionText: 'Pas de suggestions'
});
```
*Changing just a few options:*
```javascript
$.fn.magicSuggest.defaults.sortDir = 'desc';
$.fn.magicSuggest.defaults.strictSuggest = true;
```
Hope someone finds it usefull, I do ;)