Fix raw strings

[ivan-klass]

When I run my script with debugger tools connected, I got Syntax error as soon as multiavatar import is there:

>   from multiavatar.multiavatar import multiavatar
E     File "/my/home/.pyenv/versions/my-project/lib/python3.12/site-packages/multiavatar/multiavatar.py", line 23
E       regex = "\#(.*?)\;"
E               ^^^^^^^^^^^
E   SyntaxError: invalid escape sequence '\#'

The proper syntax for the regex strings defined should be r-prefixed