message: Improve documentation for errors a bit.
diff: @@ -366,9 +366,11 @@ pub trait PrimeFieldRepr: Sized +
  fn mul2(&mut self);
  }
  +/// An error that may occur when trying to interpret a `PrimeFieldRepr` as a
  +/// `PrimeField` element.
  #[derive(Debug)]
  pub enum PrimeFieldDecodingError {
  - // The encoded value is not in the field
  + /// The encoded value is not in the field
  NotInField(String)
  }
  @@ -390,6 +392,7 @@ impl fmt::Display for PrimeFieldDecodingError {
  }
  }
  +/// An error that may occur when trying to decode an `EncodedPoint`.
  #[derive(Debug)]
  pub enum GroupDecodingError {
  /// The coordinate(s) do not lie on the curve.
  