Rearrangements

Migrate to Sdk projects.
Migrate tests to xUnit.
Bump version 0.2.3.
Migrate to NetStandar2.0.

VAR.ExpressionEvaluator.Tests/ExpressionNumberNodeTests.cs

@@ -1,29 +1,28 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Xunit;
 
 namespace VAR.ExpressionEvaluator.Tests
 {
-    [TestClass()]
     public class ExpressionNumberNodeTests
     {
-        [TestMethod()]
+        [Fact]
         public void ExpressionNumberNode__One()
         {
             IExpressionNode node = new ExpressionNumberNode(1);
-            Assert.AreEqual(1m, node.Eval(null));
+            Assert.Equal(1m, node.Eval(null));
         }
 
-        [TestMethod()]
+        [Fact]
         public void ExpressionNumberNode__Two()
         {
             IExpressionNode node = new ExpressionNumberNode(2);
-            Assert.AreEqual(2m, node.Eval(null));
+            Assert.Equal(2m, node.Eval(null));
         }
 
-        [TestMethod()]
+        [Fact]
         public void ExpressionNumberNode__OneHundredDotFortyFive()
         {
             IExpressionNode node = new ExpressionNumberNode(100.45m);
-            Assert.AreEqual(100.45m, node.Eval(null));
+            Assert.Equal(100.45m, node.Eval(null));
         }
     }
 }