First cut at simplifying the API.  Renamed sevenSeg to sevenSegDigit, and sevenSegArray to plain-old sevenSeg.  Moving forward, the documented API will just be about the 'new' sevenSeg.  Set the default to just one digit.

Removed the KO binding for the old single sevenSeg, as it is pretty much useless - there only needs to be a KO binding for the new array-based sevenSeg.
Updated the demo/docs to be functional, but still need to revise the content to reflect the new simplified usage.