Blog post on using UDFs in python (#17)

* Blog post on using UDFs in python

* Addressing review comments

* Small typo

* Capitalization

* Small language adjustments

* Add more thorough description of the problem

* Variety of small readability improvements

* Update date

* Small typo

* Small change from in memory to in-memory

* Resolve remaining feedback

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Co-authored-by: Tim Saucer <[email protected]>