ExactMed 0.3.0

Added the new function exactmed_cat(), which computes mediation effects when the mediator is categorical.
In exactmed_c() when used with case-control data, the residual mean square error (MSE) has been replaced by the weighted MSE as the estimator of the error variance ($\sigma^2$) of the mediator regression model.
Documentation fixes and updates.

ExactMed 0.2.0

Added the new function exactmed_c(), which computes mediation effects when the mediator is continuous.
The function exactmed() can now calculate mediation effects with case-control data. The case-control functionality is also available with the function exactmed_c().
Added print() methods for correct display of output objects.
Documentation fixes and updates.