add set/mapcat

fix a bug where empty sets and maps returned invalid iterators

typo

Fix memory leak in sets when there is a panic

Persistent vectors implementation

Use https to download submodule

export the map module properly

add some very basic map bindings

make iteration more robust

generate readme

start working on a map type

fill out the set API

clean up directory structure

expose an umbrella module

add set union, intersection, and difference