Does this issue relate to a new feature or an existing bug?

• Bug
• [x ] New Feature

What version of Serilog is affected? Please list the related NuGet package.
2.6.0

**What is the target framework and operating system? See [target frameworks]

• [x ] netCore 2.0
• netCore 1.0
• 4.7
• 4.6.x
• 4.5.x

Please describe the current behavior?
There is no mechanism for creating a Serilog.ILogger that does nothing.

Please describe the expected behavior?
I sometimes use an optional pattern for logging in libraries such as:

        public SomeClass(ILogger logger = null)
        {
            m_logger = (logger ?? new SilentLogger).ForContext<SomeClass>();
        }

This allows consumers of the class that aren't using logging to use the abstraction without logging, while those that are can pass in a logger without having all log statements require a condition method operator. Being able to instantiate a SilentLogger makes this cheap.

Is there a better pattern with Serilog for accomplishing this?