New generates a cryptographically random string ID of length idLen,
consisting of mixed-case alphanumeric characters (A-Z, a-z, 0-9),
with no special characters or padding. The idLen parameter must be
between 0 and 255 inclusive.
NewMulti generates count number of cryptographically random string IDs of length idLen,
consisting of mixed-case alphanumeric characters (A-Z, a-z, 0-9), with no special
characters or padding. The idLen parameter must be between 0 and 255 inclusive.