modelbased 0.14.0

Changes

• The trend argument in estimate_slopes() was renamed into slope. trend
  will remain as alias.

• New function collapse_by_group(), which extracts the raw data points and
  "averages" (i.e. "collapses") the response variable over the levels of the
  grouping factor given in collapse_by. Only works with mixed models.
  Additionally, the plot() and visualization_recipe() methods get a
  collapse_group argument to use this feature when adding data points to plots
  using show_data or show_residuals.

Bug fixes

• Fixed issue in estimate_slope() when p_adjust = "esarey".

• Fixed issue in estimate_contrasts() when p_adjust = "tukey".

• Fixed error with truncated message when standard errors could not be calculated.