Converts a hexadecimal string hex into an array of bytes.
The optional separator ':' may be used between single or pairs of hexadecimal characters, eg "00:11" or "0:1". Any "0x" at the beginning
of hex is ignored. hex may not start or end with ':'.
| hex |
a string of hexadecimal characters with optional ':' separators |
|
the converted bytes, or null on error |