Call stringify() as a method, not function.

You probably want to pass the overload function as a name, rather than a coderef.  That way, will be called as a method on the object, and subclasses will have the opportunity to override it if they want.
Update text to reflect code changes.

We are passing a method name not a coderef to overload
Minor grammar error.
Merge pull request #323 from thaljef/main

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