[0.9.0] New data store method: `DataStore`

This release introduces a new method of tracking and storing data before sending it to iobeam. Please refer to new docs regarding how to use it.

Changelog

• Adding data should now be done via the new iobeam.createDataStore(columns) method,
  which allows you to track multiple streams of data in one object.
• Internally, old methods involving DataPoints and DataSeries have been converted
  to use DataStores.
• Additional documentation provided here.