Added a Serilog implementation of ILogger.

https://github.com/DamianMac/Nimbus/issues/6

A Nimbus.Logger.Serilog assembly and NuGet package, with:

`SerilogLogger` - an implementation that adapts a Serilog `ILogger` to a Nimbus one
`SerilogStaticLogger` - provides `ILogger` atop the static Serilog `Log` class
`BusBuilderConfigurationSerilogExtensions.WithSerilogLogger()` and `.WithSerilogStaticLogger()` - adds support for a Serilog logger for those not using Autofac etc.

The extensions class is in the `Nimbus.Configuration` namespace. I've found putting extension methods in their own namespaces is a bit of a usability problem for those not using R#. Let me know if you'd rather I move this to be in line with the way the Autofac one is done (also happy to reshuffle the Autofac one if you prefer this approach).

I also updated the sample with juicy coloured console output, but can't run this locally without a bus.

HTH!