message: remove writers section
diff: // //! unimplemented!()
  // //! ```
  //!
  -//! # Writers
  -//!
  -//! Writers can be used to handle parameter vectors in some way during the optimization
  -//! (suggestions for a better name are more than welcome!). Usually, this can be used to save the
  -//! intermediate parameter vectors somewhere. Currently, different modes are supported:
  -//!
  -//! * `WriterMode::Never`: Don't do anything.
  -//! * `WriterMode::Always`: Process parameter vector in every iteration.
  -//! * `WriterMode::Every(i)`: Process parameter vector in every i-th iteration.
  -//! * `WriterMode::NewBest`: Process parameter vector whenever there is a new best one.
  -//!
  -//! The following example creates two writers of the type `WriteToFile` which serializes the
  -//! parameter vector using either `serde_json` or `bincode`. The first writer saves the parameters
  -//! in every third iteration (as JSON), while the second one saves only the new best ones (using
  -//! `bincode`).
  -//! Both are attached to a solver using the `add_writer(...)` method of `ArgminSolver` before the
  -//! solver is run.
  -//!
  -// //! ```rust
  -// //! // [Imports omited]
  -// //! TODO
  -// //! ```
  -//!
  //! # Implementing an optimization algorithm
  //!
  //! In this section we are going to implement the Landweber solver, which essentially is a special
  