Function refactoring for R6 object

[program--]

Currently, all implemented functions return a tibble or character vector. These functions (and future functions) need to be refactored to return a list containing:

• the data in tibble or character vector form as currently implemented
• a query attribute
• a next attribute (if exists)
• a previous attribute (if exists)

The inclusion of query, next, and previous will allow for traversal, and easier usage of the R6 object -- particularly in the case where an end-user needs to access multiple, sequential resources, or to use the discover endpoint.

[program--]

For the query attribute, consider something similar to this:

parameters <- lapply(sys.call()[-1], deparse)
            
private$.query <- paste0(
    ifelse(nchar(names(parameters)) > 0, paste0(names(parameters), " = "), ""),
    unlist(parameters),
    collapse=", "
)