toxval 2.0.0

toxval 2.0.0 restructures the package so that every model class is handled the same way and every metric returns the same shape.
This is a breaking release: code written for toxval 1.0.0 needs changes, listed below and in NEWS.md.

Highlights

• ecx() and nsec() return a toxval tibble with one row per metric, direction and group, for brms, drc and bayesnec fits.
• Both the decreasing and the increasing direction are estimated every time.
• ecx() now supports drc fits, using parametric bootstrap replicates.
• bayesnec is now suggested rather than imported. When it is installed, ecx() and nsec() accept single fits (bayesnecfit) and model averages (bayesmanecfit).
• The new toxval_predict() generic and new_toxval_pred() constructor let a new model class be supported by writing one method.
• New vignettes define the ECx and the NSEC.

Breaking changes

• ecx_val is deprecated in favour of proportion, so an EC10 is proportion = 0.1.
• type = "relative" now measures to the asymptote of the fitted curve. What it measured before is type = "range".
• posterior and nsec_multi() are defunct. Use draws = TRUE, and nsec() on a multivariate fit.
• hormesis_def, horme, curveid and by_group are deprecated. Use group_var for grouped fits.
• Arguments after object must be named, and an unused argument is an error.
• Each ECx and NSEC reference is computed from its realisation's own control, so estimates differ from toxval 1.0.0.

See NEWS.md for the full list of changes.