message: properly use ArgminCostValue
diff: ///
  /// TODO
  use parameter::ArgminParameter;
  +use ArgminCostValue;
  /// Return struct for all solvers.
  #[derive(Debug)]
  -pub struct ArgminResult<T: ArgminParameter + Clone, U: PartialOrd> {
  +pub struct ArgminResult<T: ArgminParameter, U: ArgminCostValue> {
  /// Final parameter vector
  pub param: T,
  /// Final cost value
  @@ -14,7 +15,7 @@ pub struct ArgminResult<T: ArgminParameter + Clone, U: PartialOrd> {
  pub iters: u64,
  }
  -impl<T: ArgminParameter + Clone, U: PartialOrd> ArgminResult<T, U> {
  +impl<T: ArgminParameter, U: ArgminCostValue> ArgminResult<T, U> {
  /// Constructor
  ///
  /// `param`: Final (best) parameter vector
  