Creating multi-module projects (preparing for Pkg3)

[stevengj]

@StefanKarpinski

My immediate reaction is that the best way to handle this may be to prompt the user when there’s an import X or using X statement that doesn’t “resolve”

Just be careful about reliance on prompts and menus, because not everyone is running Julia through the REPL (e.g. you could be using IJulia, or Juno/Atom, or vscode).