Add Treasury Inspector General for Tax Administration

It's a fair amount of code since there are a few different page formats, but it's actually pretty clean.

I'm not sure what the `agency_name` should be here.
I would add to the method docstring:

This method is used to parse out the values from a raw text string containing a Javascript declaration. See an example input at the call site above.

Or something. Other than that I can't really think of anything to make it more clear either.