Changes:
* Merged pull request from FriedLabJHU to make f-strings more Pythonic. Thanks!!
* Changed `return_normalized` keyword to `normalized` in `meta.predict_pLDDT()` for consistency with other functions
* Added sanity check in case a passed sequence is an empty string (h/t Broder Schmidt)
* Added docs for the mode keyword in `meta.percent_disorder()`, so this is actually obvious to understand (h/t Broder Schmidt)
* Added several additional tests and updated the docs