Create InstanceProducer<TService>

[dotnetjunkie]

Currently the InstanceProducer class is non-generic. This means that it's GetInstance method returns object. This causes users to have to apply casting themselves if they use the InstanceProducer class as follows:

var prod = Lifestyle.Scoped.CreateProducer<DbContext>(() => new DbContext("constr"), container);

container.RegisterSingle<IUnitOfWork>(
    new DbContextUnitOfWork(() => (DbContext)prod.GetInstance()));

If the Lifestyle.CreateProducer<T> methods would return an InstanceProducer<T> instead, this would make scenarios like these much cleaner, because that would allow the user to minimize the code to the following:

var prod = Lifestyle.Scoped.CreateProducer<DbContext>(() => new DbContext("constr"), container);

container.RegisterSingle<IUnitOfWork>(new DbContextUnitOfWork(prod.GetInstance));