API docs generation

Generated docs for https://nlog-project.org/documentation/

How to run

1. Perhaps update the year. Search for 2004- for in NLog.shfbproj.
2. Run BuildDoc.cmd
3. Copy the Doc folder to the documentation folder of nlog.github.io
4. Remove unneeded files: .config, .aspx. .php, WebKI.xml, WebTOC.xml and LastBuild.log