Added the C source for the light sensor with necessary changes to cmake,
examples, docs.
* Renamed all files with grovelight to light
* Replaced all instances of grovelight with light
* Added C source for light sensor
* Updated all cmake files
* Added C example for light sensor
* Split out light sensor from grove library
Signed-off-by: Noel Eck <noel.eck@intel.com>
