Changed the output to be the fit model, like in scikit-learn, instead of the total improvement, to allow for chaining

Added in callback functionality to both the fit and from_samples methods

and methods Added in the return_history parameter to both the fit and from_samples methods, which will return the history callback as well as the fit model

parameter to both the and methods, which will return the history callback as well as the fit model Resolved an issue in the summary method where default weights were assigned to the wrong variable when not passed in.

method where default weights were assigned to the wrong variable when not passed in. Resolved an issue where printing an empty model resulted in an error.