param fun consistent naming

[lwarode]

• consistent naming of function and method parameters with consistent description of parameters (grouping_vars vs group_var --> grouping_vars & grouping_var or group_vars and group_var)
  e.g. #' @param grouping_vars A character vector containing grouping variables of a data table. vs. #' @param group_var Categorical variable that is used to group the metric variable visually.

• either highlight object type as code or not, but stay consistently
  #' @param db (character character string of the connection arg) vs #' @param group_var Categorical variable that is used to group the metric variable visually.