Shorthand for binding to the same type

...to be used inside `Bindings` implementations, e.g.:

```php
// Repetitive
$inject->bind(Implementations<DataSource>::class, new Implementations<DataSource>(/* ... */));

// Maybe something like this?
$inject->instance(new Implementations<DataSource>(/* ... */));
```

This would be consistent with the `UseBindings` DSL, see #23 