Added and update resources on C# (#3958)

* Added C# book resource

* Updated "C# Programming Yellow Book" resource

Added more info on the resource

* Changed resources in alphabetical order

Previous commit failed in PR tests

* Alphabetical sort again

free-programming-books.md

@@ -1043,8 +1043,9 @@ Kerridge (PDF) (email address *requested*, not required)
 * [C# Notes](https://goalkicker.com/CSharpBook) (PDF)
 * [C# Notes for Professionals](http://books.goalkicker.com/CSharpBook/) - Compiled from StackOverflow documentation (3.x)
 * [C# Programming](https://en.wikibooks.org/wiki/C_Sharp_Programming) - Wikibooks
+* [C# Programming Yellow Book](https://www.robmiles.com/s/CSharp-Book-2019-Refresh.pdf) - Rob Miles (PDF)(2019)
+* [C# Smorgasbord](https://www.filipekberg.se) - Filip Ekberg (HTML) [(PDF, EPUB, MOBI)](https://www.filipekberg.se/2018/04/02/csharp-smorgasbord-free/) (2018)
 * [C# Tips](https://leanpub.com/cstips) - Jason Roberts *(Leanpub account or valid email requested)*
-* [C# Yellow Book](http://www.csharpcourse.com) (intro to programming)
 * [Creating Mobile Apps with Xamarin.Forms C#](https://developer.xamarin.com/guides/xamarin-forms/creating-mobile-apps-xamarin-forms/)
 * [Daily Design Patterns](https://web.archive.org/web/20170930132000/https://www.exceptionnotfound.net/downloads/dailydesignpattern.pdf) - Matthew P Jones (PDF)
 * [Data Structures and Algorithms with Object-Oriented Design Patterns in C#](https://web.archive.org/web/20161220072449/http://www.brpreiss.com/books/opus6/) - Bruno Preiss