Incorrect suggestion for Character.isXxx

[lunagl]

Description

All three "known ranges" listed in #73 are incorrect, since the Character functions work not only with ASCII, but other unicode codepoints as well. Their respective documentation lists all the character classes they accept.

This is problematic when students are relying on the fact that they are working with an ASCII character from a specific numeric range (say for indexing into an array).
If other characters are explicitly supposed to be handled, then functional tests should probably check such cases to prevent students from relying on ASCII in the wrong places.