The test corpus for 10 (find unique words) has a lot of words that are not detected correctly by the solution

The solution to problem 10 (find unique words) considers a "word" to be anything that matches the pattern `r"[0-9a-zA-Z-']+"`

Alas, there are many words in shakespeare.txt that contain words outside of this pattern. The first few are:

- Personæ
- Phœbus
- dæmon
- Cæsar
- Æneas

These are mis-detected as

-`'Person'`
-`['Ph', 'bus']`
-`['d', 'mon']`
-`['C', 'sar']`
-`'neas'`