Grapheme & Byte-based String Iterations

We also need to come up with a syntax for iterating a string by graphemes, and possibly byte-based iterations too. I think we could use string methods that return arrays for this:

for grapheme in @graphemes(string)
    echo $grapheme
end

for char in @chars(string)
    echo $char
end

for byte in @bytes(string)
    echo $byte
end