message: remove useless phantomdata
diff: /// TODO DOCUMENTATION
  ///
  -use std::marker::PhantomData;
  use errors::*;
  use parameter::ArgminParameter;
  use ArgminCostValue;
  -// use std::default::Default;
  /// This struct hold all information that describes the optimization problem.
  #[derive(Clone)]
  @@ -23,8 +21,6 @@ pub struct Problem<'a, T: ArgminParameter + 'a, U: ArgminCostValue + 'a, V: 'a>
  pub upper_bound: T,
  /// (non)linear constraint which is `true` if a parameter vector lies within the bounds
  pub constraint: &'a Fn(&T) -> bool,
  - /// We don't really need V
  - _marker: PhantomData<&'a V>,
  }
  impl<'a, T: ArgminParameter + 'a, U: ArgminCostValue + 'a, V: 'a> Problem<'a, T, U, V> {
  @@ -45,7 +41,6 @@ impl<'a, T: ArgminParameter + 'a, U: ArgminCostValue + 'a, V: 'a> Problem<'a, T,
  lower_bound: lower_bound.clone(),
  upper_bound: upper_bound.clone(),
  constraint: &|_x: &T| true,
  - _marker: PhantomData,
  }
  }
  