more detail about writing model class
more detail about writing model class

* list layers using model parameter
* subclass model to Model
* use tuples to pass arguments to classes
* list classes as list of sources
* optional to provide layer arg, b/c model already knows layer classes

Signed-off-by: Mark Mikofski <318ee9014fd8bbcb598d57c182125ac60961dfd8@sunpowercorp.com>

SunPower/Carousel,mikofski/Carousel,mikofski/Circus