* NLog.config: added NLog configuration

* NLog.xsd: added NLog schema

* packages.config: added NLog configuration and schema

* ConfigurationAdapter.cs: added exception

* App.config: added option to select type of markdown outpu

* DocToMarkdown.csproj: added nlog config and schema

* MarkdownType.cs: added integer values

* Program.cs: added option to get type of markdown output from
  app.config
Edited README.md