Multi-file examples

Minimum Rust version: 1.22

Cargo has an examples feature for showing people how to use your package. By putting individual files inside of the top-level examples directory, you can create multiple examples.

But what if your example is too big for a single file? Cargo supports adding sub-directories inside of examples, and looks for a inside of them to build the example. It looks like this:

     └── // code here
     └── // a single-file example
     └── complex-example
        └── // a more complex example that also uses `helper` as a submodule