Feature request: Document internal functions

[Hugovdberg]

A lot of internal functions are not documented at all. By documenting the functions it is easier to follow the thinking of other developers when reading a piece of code. Marking the functions as internal using @keywords internal allows the functions to be documented without adding an entry in the index. However, the documentation is available to both users and developers if they specifically request it. Also, tooltips in RStudio are filled with this documentation.

[Hugovdberg]

TODO:

• add roxygen documentation to each function
• add @keywords internal
• add @rdname internal<functionname> where <functionname> is replaced with the actual function name. This prevents errors because rd-filenames starting with a . are invalid.

[Hugovdberg]

Documentation was added with #243, closing this issue.