Character normalization

[jacksgt]

As Eelis mentioned:

I've seen some utf-8 characters being used in place of similar looking ascii characters. We might want to do some character normalization before this. Example package: https://github.com/woodgern/confusables

Originally posted by @EelisK in #22 (comment)

So we should look into character normalization at least for get_term_set, but also think about if the regular table cells and headers need to be normalized.

[jacksgt]

This has been partially implemented in #33
Still needs to be extended to the relation and headers we are extracting.