Call search api multiple times if not enough links were found (fixes #51)

After parsing the Search API results the number of links will be checked and if there aren't enough links yet, we'll try to get more tweets. We're using Search API's `max_id` param to retrieve only tweets tweeted before the last results (i.e. paginate over the results).

Search API requests are limited to 10 for every hashtag right now as we don't want to send too many requests (this is configurable through `maxSearchApiRequests`)