Add simple interface

[CumpsD]

Not sure if this is something you would be interested in, a simple usage to run only one instance of an app

No offence if you dont think this PR should make it into master, it's something we needed :)

Usage:

    public class Example
    {
        public void Main()
        {
            var distributedLock = new DistributedLock<Example>(new DistributedLockOptions
            {
                Region = RegionEndpoint.EUWest1,
                LeasePeriod = TimeSpan.FromMinutes(5),
                ThrowOnFailedRenew = true,
                TerminateApplicationOnFailedRenew = true
            });

            if (!distributedLock.AcquireLock())
            {
                Console.WriteLine("Could not get lock, another instance is busy");
                return;
            }

            // Do stuff

            distributedLock.ReleaseLock();
        }
    }