Migrate to Sdk projects.

* BasicBlockChain.Core.
* BasicBlockChain.Core.Tests.
* Migrate MSTests to XUnit.

BasicBlockChain.Core/Properties/AssemblyInfo.cs

@@ -1,5 +1,4 @@
 using System.Reflection;
-using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 // General Information about an assembly is controlled through the following
@@ -10,7 +9,7 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyConfiguration("")]
 [assembly: AssemblyCompany("")]
 [assembly: AssemblyProduct("BasicBlockChain.Core")]
-[assembly: AssemblyCopyright("Copyright ©  2020")]
+[assembly: AssemblyCopyright("Copyright © VAR 2020")]
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]