message: Document return value of config_value_field::set
diff: @@ -47,7 +47,8 @@ public:
  // -- modifiers --------------------------------------------------------------
  - /// Sets this field in `object` to `x`.
  + /// Tries to set this field in `object` to `x`.
  + /// @returns `true` on success, `false` otherwise.
  virtual bool set(Object& object, const config_value& x) const = 0;
  /// Restores the default value for this field in `object`.
  