Allow Anomalies() to work when hcst and obs have different lat/lon dimensions
In the case that the anomalies must be computed before Downscaling or other operations that require hcst and obs to be in their original grids, CST_Anomaly() cannot be used. The problem is described in s2dv#108 (closed).
The proposed solution, at least for now, is to add the option to compute the anomalies with a simple mean in this particular case. If the user has requested cross-validation or other special methods, they will get a warning stating that these methods are not currently available for the case where hcst and obs have different grids.
The changes will be made in the branch dev-anomalies-downscaling.