Source Release project configuration and Statistics printing

+ Support for generating a source-only NuGet package by specifying the Source Release project configuration.
+ Added preprocessor directive to ignore the file NativeMethods.cs when building against .NET Core.
+ Added support to the logging facilities for printing statistics to the log files when they are being closed.
– Improved readability on preprocessor directives for the visibility selectors of the Logging facilities.
– Fixed and updated some member documentation.
– Enabled xmldoc generation for the project.

See the full commit on Bitbucket https://bitbucket.org/kderazorback/razorsoftware.logging/commits/3aa43d3ff5e838c5ccc3d967242fcf1fedb3b3f6