Functional `column.data` and `dataSchema`

In the same vein as:
- https://github.com/warpech/jquery-handsontable/issues/261
- https://github.com/warpech/jquery-handsontable/pull/435

I am using handsontable with backbone (and backbone-relational), and would like to make use of the events, etc. that are only available when using their "property"-style interface.

This pull includes some doc updates, with an example of the usage of a small model `data`.