157 new function label extracter

[SanderDevisscher]

This pull request introduces a new utility function for extracting columns from the DMOGG dataset based on labels, improves documentation, and makes minor enhancements to dependencies and internal data loading. The most significant change is the addition of the label_extracter function, which provides flexible options for selecting columns and optionally joining presence information for labels.

New feature: Data extraction utility

• Added a new function label_extracter that allows users to extract specific columns from the DMOGG dataset based on provided labels. The function supports multiple modes for column selection ("all", "select", "list", "group"), can join presence information, and is fully documented with usage examples. [1] [2] [3]

Documentation improvements

• Added Roxygen2-generated documentation for label_extracter, including parameter descriptions, details, and usage examples.
• Fixed a minor typo in the documentation for label_selecter regarding the label_type parameter. [1] [2]

Dependency and internal loading updates

• Added purrr to the Suggests field in the DESCRIPTION file to support new functionality in label_extracter.
• Updated label_selecter to use the read_dmogg() function for loading the georeferenced DMOGG dataset, ensuring consistency and maintainability.

[martijn-bollen]

For both examples 1 and 3, I receive an error related to the column: 'label_nummer_samen'. For the specific error messages read below.

Note: in example 3, I recieve the exact same error when removing 'label_nummer_samen' from the vector specified in the column_list argument (i.e. c("onderkaaklengte_comp", "geslacht_comp") instead of c("label_nummer", "onderkaaklengte_comp", "geslacht_comp"))

All these issues should be fixed by adding the missing package declarations