Encoded string to decode.
A decoded normal string.
{
    immutable password = "base64:aGFyYmwgc25hcmJsIDEyMzQ1";
    immutable decoded = decode64(password[7..$]);
    assert((decoded == "harbl snarbl 12345"), decoded);
}
{
    immutable password = "base64:";
    immutable decoded = decode64(password[7..$]);
    assert(!decoded.length, decoded);
}
Base64-decodes a string.
Merely wraps std.base64.Base64.decode and std.string.representation into one function that will work with strings.