Confirm that arguments to paired @begin and @end comments match

[tmcphillips]

Our example.py script contains an instance of the @begin tag not matching the corresponding @end tag. YW should detect this during the extract phase and report it as a warning (or error?).

[swanskysong]

I found the following block has this conflict:

"pound sign" "pound sign" @ begin standardize_with_mask
...
"pound sign" "pound sign" @ end standardize_mask

Is this the one we're referring to? I think in our first prototype, we're not targeting to have the YW validation module, so we should fix this issue manually. We can use this as an example for the YW validation module in the future.