BaseSet 1.0.0

Now it is possible to list sets and elements that are not present in the relations but might be on the object via its factors: name_sets(), name_elements(), nElements() and nSets() gain a all argument.
Fix a problem with $<- when the length did match a slot but the name didn’t.
Now it is possible to use sets and elements to subset a TidySet (but not for relations).
New dimnames() and names() functions to discover the names of the data in the slots.
Minor changes to getGAF() to improve speed.
Increase R version dependency to 4.1 to remove magrittr dependency.

BaseSet 0.9.0

tidy() now defaults to tidySet().
New function union_closed().
Make more robust the code to unwanted dimensions drops.
power_set() returns also the sets of size 1 and have better names by default.
Extractors [, $, [[ and setters [<-, $<-, [[<- now work for TidySets:
- i indicates rows,
- j either “relations”, “sets” or “elements”
- k the columns of the slot.
However TS[["A"]] extracts set “A” and replacing it via [[<- will remove it.
Completion of $ works.
length() returns the number of sets (to complete ncol and nrow).
lengths() returns the number of relations for each set.