Gets an array of unique items from the current array.
@param {Array} a The Array object to operate on.
@returns {Array} A new array with no duplicate values.
@function
function unique (a) {
                    if(!(a instanceof Array)) return a;

                    var visited = [],
                        unique  = [];

                    libs.object.each(a, function (item) {
                        if(visited.indexOf(item) === -1) {
                            unique.push(item);
                            visited.push(item);
                        }
                    });
                    return unique;
                }