"is" operator.

test/class_new.wren

@@ -0,0 +1,4 @@
+class Foo {}
+
+var foo = Foo.new
+io.write(foo is Foo) // expect: true

test/class_syntax.wren

@@ -0,0 +1,7 @@
+// Empty body.
+class A {}
+
+// Newline body.
+class B {
+
+}

test/is.wren

@@ -0,0 +1,16 @@
+io.write(true is Bool) // expect: true
+io.write((fn 1) is Function) // expect: true
+io.write(123 is Num) // expect: true
+io.write(null is Null) // expect: true
+io.write("s" is String) // expect: true
+
+io.write(Num is Bool) // expect: false
+io.write(null is Class) // expect: false
+io.write(true is Function) // expect: false
+io.write((fn 1) is Num) // expect: false
+io.write("s" is Null) // expect: false
+io.write(123 is String) // expect: false
+
+// TODO(bob): Non-class on RHS.
+// TODO(bob): Precedence and associativity.
+// TODO(bob): Metaclasses ("Num is Class").