create an ensemble method to compute Vincent/quantile average ensemble based on more output types

[elray1]

Currently we have a linear_pool function that works with multiple output types, and a simple_ensemble function that computes linear pool or Vincent ensembles based on the output type. However, we don't have the ability to compute Vincent ensembles for any output type other than quantile. The proposal is to add a function named vincent or quantile_average that computes Vincent ensembles based on other output types