Meta-estimators for consensus prediction

[vruusmann]

We are looking to ensemble different models using several rules, for example, multiplying the results of two models and averaging the product with the result of a third model.

There could be a meta-estimator class that combines the predictions of child estimators based on some formula. The simplest meta-estimator configuration would be the one that accepts two estimators as arguments; all other meta-estimator configurations can be derived from this one via nesting.

For example:

regressor = ConsensusRegressor(regressor1, regressor2, formula = "(y[0] + y[1]) / 2")