Add statuses/lookup entry point

[dfliess]

Hi,
Here you have the code if you would like to use /statuses/lookup entry point

/*
 * LOOKUP Statuses /tweets by ids
 */
Twitter.prototype.lookup = function(ids, params, callback) {
    if (typeof params === 'function') {
        callback = params;
        params = {};
    }

    if ( typeof callback !== 'function' ) {
        throw new Error('FAIL: INVALID CALLBACK.');
        return this;
    }

    var url = this.options.rest_base + '/statuses/lookup.json';
    params = utils.merge(params, {id:ids});
    this.get(url, params, callback);
    return this;
}