Serilog.Extras.MSOwin - allows logging of MS.Owin.* stack via Serilog

An 'extras' lib that provides an Microsoft.Owin.Logging.ILoggerFactory implementation to allow logging via Serilog from the various MS.Owin.* packages (aka katana).

Also includes middleware that allows opening of a nested diagnostic context to help with correlating of log messages in an owin pipeline. See https://github.com/damianh/serilog/blob/470f89b19b6b63ccc33c6f1e55ccd4fa02cf28b3/test/Serilog.Extras.MSOwin.Tests/Extras/MSOwin/RequestContextMiddlewareTests.cs as example. This middlware is not MS.Owin specific though - it could go into a Serilog.Extras.Owin project. Let me know if you would prefer that.

Let me know if doesn't match any style concerns, convetions etc . I tried to keep it consistent.

Am not too worried if you decide to not pull it in, will be using this code anyway just thought it would be useful for others :)