Make IBackgroundJobClient public

[odinserj]

Static methods such as BackgroundJob.Enqueue are good to demonstrate things and for quick starts. But they complicate unit tests and can not be extended using extension methods. Moreover, BackgroundJobClient can be used to batch multiple jobs without creation connection for each.

[odinserj]

Completed, API looks like BackgroundJob.* methods:

IBackgroundJobClient client = new BackgroundJobClient(); /* There are different overloads */
client.Enqueue(() => Console.WriteLine("Hi"));
client.Schedule(() => Console.WriteLine("Delayed"), TimeSpan.FromMinutes(5));
client.Dispose();