Added class usage sample

Author: Ary Borenszweig

samples/class.cr

@@ -0,0 +1,14 @@
+class Foo
+  def initialize(x)
+    @x = x
+  end
+
+  def x
+    @x
+  end
+end
+
+f1 = Foo.new 1
+f2 = Foo.new 2.0
+
+puts(f1.x + f2.x)