Find a version of the Dale-Chall vocabulary list that is able to understand inflections

[nonprofittechy]

Currently, even if the root word is easy, an inflection of the word can be marked as difficult. We should change this.

There is an issue that offers suggestions to fix this in the parent library we use, textstat: textstat/textstat#150

[nonprofittechy]

Also check out https://github.com/public-law/readability

[nonprofittechy]

Finally, want to note here that we intend to eventually replace the Dale-Chall wordlist with our own wordlist. So whatever we do with "stemming" should be generalizable.