Implement auto registration

[ltackmann]

Scan through libraries for classes implementing interfaces

[jimsimon]

I don't think this would be too difficult to do and I might pick it up. I think there might need to be support for detecting named injection targets via annotation:

class CoolInterface {
  ...
}

class DefaultCoolImpl implements CoolInterface {

  @inject
  DefaultCoolImpl () {}
  ...
}

@Named('other-cool')
class OtherCoolImpl implements CoolInterface {

  @inject
  OtherCoolImpl () {}
  ...
}

class ConsumingClass {
  CoolInterface otherCool;  

  @inject
  @Named('other-cool') // Does this need to go next to the parameter type?
  ConsumingClass (this.otherCool);
}

main () {
  var injector = new Injector(new AutoDiscoveryModule())
}

I also think it should only autoregister resources marked with an @inject and not necessarily all classes implementing interfaces (since it should be possible to inject something that doesn't have an interface).