This decodes a UTF-8 string into a table of Unicode numbers.
The function returns a (numerically-keyed) table of numbers, one for each Unicode code point found in the UTF-8 string argument. If the string is found to not be valid UTF-8 it returns nil.
eg.
t = utils.utf8decode (utils.fromhex ("E18E88"))
print (t [1]) --> 5000