Improving REMIT availability

We have added four new API endpoints for period-based series. Some explanation might be useful: A time-series, is defined as values at fixed time-step, say hourly, daily, weekly. The REMIT info, however, is issued as period series, meaning capacity from a timestamp to a time stamp. Our API converts the period- to time-series on the fly. In effect, it makes the REMIT data user-friendly.