SAIL fixed, rearrangement of function calls

A bugfix release. The code to call SAIL (i.e., not PROSPECT+SAIL) was buggy. I think it now works (but requires more testing than the one I could be bothered with).

Also, note that the calls to the canopy models have changed. They should be more streamlined, and they also allow you to get access to SDR, BHR, DHR and HDR.

The soil model can be overridden by passing a soil reflectance spectrum, but you can still use the old model (dry/wet soil) if you want to. This should make it easier to implement your model outside of the bindings (but remember that we still assume a Lambertian soil!)