Implemented scopes

tests/integrations/test_scopes.toy

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+//shadowing
+var answer = 42;
+print answer; //42
+{
+	    var answer = 7;
+		    print answer; //7
+}
+print answer; //42
+
+//rebinding
+var question = 42;
+print question; //42
+{
+	    var question = question;
+		    print question; //42
+}
+print question; //42
+
+//TODO: scope test case