Use compilation tracers to store modules bytecode

[josevalim]

We need to associate the module to a cell and write it to disk. The path in disk will be added to the code path. Before a cell is reevaluated, we can delete the file and purge/delete the module.

This will allow documentation and doctests to work for Livebook modules. /cc @BrooklinJazz

[josevalim]

Wild idea: we could use this to automatically extract doctests, run them inline, and provide direct used feedback.

[BrooklinJazz]

🎉🎉🎉🎉🎉🎉