Insert and Update methods for Model

[gingo]

Please allow calling update() and insert() on model directly to avoid calling exists(), when one knows what kind of operation should be performed. Current implementation of save method is real performance killer.

[lsjwzh]

u r right. I guess emilsjolander is too busy to maintain this......
I open a fork https://github.com/lsjwzh/sprinkles and add some features.
I think we could implement this at my fork first.