Observables - Githubissues

This PR includes a few things:

Support of callable structs and closures. It still may not be perfect.
Detection of circular references. Those are not supported in WebAssembly, so a default value is plugged in.
Better support of object that alias. Before, there were cases where the compilation ended up making copies.
In JS.h, fix multiple keyword arguments.
An example using Observables to generate an SVG. This includes code to help with compilation of a set of Observables with their listener methods.

tshort / WebAssemblyCompiler.jl