[~keithbostic] Please review these changes for huffman. I added a test for all the valid huffman config settings as well as invalid ones.
There was one minor bug fix to reset ret after reading the utf file.
One outstanding issue is I found in my test that I could not use hex in the frequency file as shown in the docs. SCNu64 does not read hex. You'll notice test_huffman01.py writes decimal. We can fix the documentation or assume the values are hex, fix the code and document that requirement.