ldb prints out Unicode characters
When printing out a base-char, only the low 8 bits of the code were used. But with Unicode support, we need to take all the bits and print them out. For control codes we use the form "#^x". (Was #\C-x, which isn't a valid supported character form.) Ascii is printed as normal "#\a", and everything else use uses "#\u+".
While we're at it, we also added special cases like #\Vt that are listed in https://cmucl.org/docs/cmu-user/html/Characters.html#Characters.
With this, we can print out all unicode characters in a form that can be pasted back into lisp.