Support named loggers

- Updated API to support named loggers
- Added loggers for NLog and log4net

Note that you can set the logger factory to be used like:
Logger.Factory = new NLogLoggerFactory();
NuGet build targets for logging integration

- NuGet build targets for logging integration
- Updated samples for new logging API
- Up-revved to version 0.1.12.8 (have to specify a Chinchilla version in
dependencies section of new NuGet logging integration packages)
Merge pull request #9 from cocowalla/master

Update logging API to support named loggers