Bel strings think in bytes, not characters

[masak]

This:

$ perl -Ilib bin/bel
Language::Bel 0.46 -- msys.
> (len "¦")
2

Should be 1.

[masak]

Reading perldoc perluniintro and perldoc perlunicode, it seems like the following changes are warranted:

• binmode on file handles (maybe?)
• use utf8
• use feature 'unicode_strings'