Accept `Vec<T>` as function arguments

[domoritz]

It would be great to accept vectors of objects (especially vectors of objects created by wasm bindgen itself). I believe that the workaround right now is to create a builder that has a method to add a new T, which one has to call for each entry in the vector.

Follow up for comment by @fjarri in #111 (comment)

See nucypher/rust-umbral#23 for an example.