Convert to and from Hex strings.
Convert a hexdecimal string such as "abc94f" to a decimal integer.
Hex.fromString "a5" == Ok 165 Hex.fromString "hat" == Err "invalid hexadecimal string"
Convert a decimal integer to a hexdecimal string such as "abc94f".
"abc94f"
Hex.toString 165 == "a5"
Convert a hexdecimal string such as "abc94f" to a decimal integer.