silviculture 0.2.0

This new version brings new naming conventions that will be useful for sorting the package into "modules" of related functions.

silv_tree_*(): tree-level metrics (although some can be also used as stand-level using the ntrees argument).
silv_stand_*(): stand or plot-level metrics
silv_predict_*(): predictions based on models

The old functions are now deprecated and will be eliminated in a future release.

New functions

silv_density_sdi(): calculates the Stand Density Index
silv_predict_height(): estimates height from diameter, using the so-called h-d curves. The argument equation allows to choose which equations to use. Currently, only eq_hd_aitor2025() available.
silv_stand_dominant_diameter(): calculates dominant diameter using two methods:
- Assman: the mean diameter of the 100 thickest trees per hectare
- Weise: the quadratic mean diameter of the 20% thickest trees per hectare
eq_biomass_*(): equations to be used inside the model argument of silv_predict_biomass().

Fix an error with the validator of variable names in silviculture::Inventory S7 class.
biomass_models: some were failing because the "-" sign was parsed as an em dash.

Prediction functions (silv_predict_*()) will now have common arguments, and specific arguments that depend of the model used that are specified as a function (e.g. silv_predict_height(model = eq_hd_aitor2025())).
silv_volume(): it assumed diameter to be in meters. Now the diameter must be given in centimeters. An informing message was added to the function.
S7 silviculture::Inventory class now stores groups.

silv_diametric_class() deprecated in favour of silv_tree_dclass()
silv_basal_area() deprecated in favour of silv_tree_basal_area() and silv_stand_basal_area()
silv_volume() deprecated in favour of silv_tree_volume()
silv_dominant_height() deprecated in favour of silv_stand_dominant_height()
silv_lorey_height() deprecated in favour of silv_stand_lorey_height()
silv_sqrmean_diameter() deprecated in favour of silv_stand_qmean_diameter()
silv_spacing_index() deprecated in favour of silv_density_hart()
silv_ntrees_ha() deprecated in favour of silv_density_ntrees_ha()
silv_biomass() deprecated in favour of silv_predict_biomass()