add example for section names with question marks

examples/keys_with_questionmarks.html

@@ -0,0 +1,3 @@
+{{#person?}}
+  Hi {{name}}!
+{{/person?}}

examples/keys_with_questionmarks.js

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+var keys_with_questionmarks = {
+  "person?": {
+    name: "Jon"
+  }
+}

examples/keys_with_questionmarks.txt

@@ -0,0 +1 @@
+  Hi Jon!