Adds tostring and type functions

UpsilonTests/StandardLibraryTests/BasicFunctionsTests.cs

@@ -73,5 +73,32 @@ return value
             Assert.Empty(script.Diagnostics.Messages);
             Assert.Equal(284, result);
         }
+
+        [Fact]
+        public void ToStringTest()
+        {
+            const string input = @"
+return tostring(100)
+";
+            var script = new Script(input, BoundScope, StaticScope);
+            Assert.Empty(script.Diagnostics.Messages);
+            var result = script.Evaluate<string>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal("100", result);
+        }
+
+        [Fact]
+        public void TypeTest()
+        {
+            const string input = @"
+return type(100)
+";
+            var script = new Script(input, BoundScope, StaticScope);
+            Assert.Empty(script.Diagnostics.Messages);
+            var result = script.Evaluate<string>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal("Number", result);
+        }
+
     }
 }