CFG preview tool for browser

[hansihe]

In order to gain interest in the project, its really important that people can very quickly start tinkering with something interesting.

A good way to do that would be to implement a browser tool, possibly similar to godbolt, where the user can enter their elixir/erlang/core erlang code on the left, and see a graph/textual representation of EIR on the right.

Compiling EIR itself to webassembly won't be much of an issue, but in order to be able to easily enter elixir or erlang directly, I think we need to have a backend of some sort.