Lake model sample data

[tbohn]

@jhamman asked me if I could provide some sample data for the lake model. I think the primary goal was for incorporating into the travis build unit or science tests. But perhaps it's also useful to users as sample data.

I'm preparing data for Findley Lake, which researchers at UW (including Jeff Richey and Dennis Lettenmaier) studied for a while in the 1970s. I haven't found detailed observations, but Richey and Wissmar (1979) published some estimates of seasonal in/out fluxes for 1974 and 1975. I've taken some sparse data about lake bathymetry and fit a simple curve to get a depth-area relationship. So it should be close enough for us to confirm whether the model is getting reasonable results.