* Improved `plot_effect()` and `plot_stress()`. You can now control whether the observed values (the points) should be plotted using the `which` argument.
* Renamed `sys_tox_not_fitted` and `sys_tox_env_not_fitted` to `sys_tox_observed` and `sys_tox_env_observed` in the output of `ecxsys()`.
# stressaddition 2.3.0
*`predict_mixture()` accepts multiple values for the concentration of the second toxicant. Both concentration vectors must be the same length.
*`predict_mixture()` returns a data frame with the concentrations and effects. Previously it was only a vector of effects.
*`predict_mixture()`now returns a data frame with the concentrations and effects. Previously it was only a vector of effects.
*`predict_mixture()` received a new argument "effect_max" which scales the returned effect values.
* Renamed the arguments of `predict_mixture()` to use underscore letters a and b instad of 1 and 2. For example model_1 is now model_a.
