Add a mechanism for immediately instantiating providers that need not be lazy.

This is for cases where the provider does some work upon its instantiation (like registering itself).

This PR will expose `Bottle#digest` to be used as such:

Assume the following services are registered: `logger`, `printer`.

```javascript
var services = Bottle.digest(['logger', 'printer']);
// services[0] === Bottle.container.logger
// services[1] === Bottle.container.printer