Handle if statements

UpsilonTests/IfTests.cs

@@ -0,0 +1,18 @@
+using Upsilon.Evaluator;
+using Xunit;
+
+namespace UpsilonTests
+{
+    public class IfTests
+    {
+        [Fact]
+        public void BasicIfTest()
+        {
+            var input = "if true then val = true end";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            var actual = script.Evaluate<bool>();
+            Assert.True(actual);
+        }
+    }
+}