if target is null, we'll try to minimize the turnover metric
turnover_objective(name, target = NULL, arguments = NULL, multiplier = 1,
enabled = TRUE, ...)name of the objective, should correspond to a function, though we will try to make allowances
univariate target for the objective
default arguments to be passed to an objective function when executed
multiplier to apply to the objective, usually 1 or -1
TRUE/FALSE
any other passthru parameters
an objective of class 'turnover_objective'
if target is set, we'll try to meet the metric