Better documentation 📝

[jakobbossek]

• For some weird reason, for the return value of a function, the indentation seems broken.
• Not happy anymore with the way expected data types for arguments are stated. E.g. x [numeric(1)] might be clear for an experienced user, but not a less experienced R rookie.
• Currently, many technical details are given in the @description field. This should rather go under @details, right? Description should hold some information on what the function actually does.
• There should be DOIs for all referenced papers and DOIs should be links.
• Sometimes titles have a trailing dot, sometimes not. What is the recommendation here?
• It looks weird if for the return value only the data type is reported. We should do this more R-like even if the result is obvious.
• Function hv lacks a reference.
• Examples for log_init need line-breaks
• The index looks very full due to @seealso and @family.