IEx autocompletion should support identifiers that include numbers

Closes #1337
Adding Set with simple ops just for bucket (small sets)
delete from a set
I think member is a better name than value
Adding set union
Adding set intersection for buckets
Adding set difference for buckets
Adding set member? for buckets
put supports growing into a trie.
* to_list works with trie
Support expanding depth of nodes.
There is a lot of CRAZY resizing logic that is copied from HashDict. Once everything is working consider extracting.
member? for sets works with nodes
union works with nodes
delete works with nodes
nodes also don't contain duplicates
Correcting a bad merge
documentation for functions.
Refactor: removing unneeded comparisons
difference and intersection support for nodes.
Though not very efficient for nodes.
Corrected definition of difference.
Set 1 minus Set 2 members.
formatting tweaks