Use the Display trait if it's satisfied, fallback to Debug otherwise, and
if neither are implemented use a default string value.
The typical "nice" way to display things is via the Display trait. However, sometimes
this trait is not available, but Debug is. Debug is easy to derive. In those cases
it would be nice to use Debug as a fallback.
```rust use visual::{vis, Visual};
fn main() {
// The vis! macro wraps your type in such a way that it can decide which trait to
// use: Display, Debug or neither
printer(vis!("hello")); // &str implements Display, so use it
printer(vis!(vec![1, 2, 3])); // Vec does not, but it impls Debug, so we use that
struct MyStruct;
printer(vis!(MyStruct)); // `MyStruct` impls neither, so we use a default string value
}
fn printerVisual wrapper around your type
println!("{}", t.get_display()); // Use get_display to get a string representation of your type
}
```
If neither trait is implemented, the string representation will be the one defined by
visual::get_non_displayable_string(). This default label can be initialized to a custom value
once, by calling visual::set_non_displayable_string("value").
For the magic to work, I use the "autoderef hack" proposed by Lukas Kalbertodt, which in turn is based on David Tolnay's technique.