Sibling modules and traits

[arnaudgolfouse]

@2e71828

There needs to be exactly one mod printable; statement in your project.

That could be misleading: you can have

• In main.rs:

  mod printable;
  fn main() {}
  

• In printable/mod.rs:

  mod printable;
  

• And a printable/printable.rs file.

In the same way that the same file name can appear multiple times in the filesystem.