Feature/basic evaluator (#3)

* Refactor

* Updated TreeNode system to use abstract base class and inheritence

* Updated unit test coverage

* Improved code coverage

* Added missing files

MathEngine/EngineTests/Parser Tests/Nodes/NodesTests.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace EngineTests.Parser_Tests
+{
+    /// <summary>
+    /// Class for testing the TreeNodes
+    /// </summary>
+    [TestClass]
+    public class NodesTests
+    {
+        /// <summary>
+        /// Test the Parser on a basic List of tokens
+        /// </summary>
+        [TestMethod]
+        public void TestParserBasicExpression()
+        {
+
+        }
+    }
+}