RFC 1924 describes a compact, fixed-size representation of IPv6
addresses which uses a base 85 number system. This module handles
some of the uglier details of it.
The base 85 numbers (from 0 to 84) are as follows:

`
`

`
0..9 A..Z a..z ! # $ % & ( ) * + - ; < = > ? @ ^ _ ` { | } ~
`

At the moment, there’s not much in this module. But it should be
sufficient for the purposes of RFC 1924.

This module has a variable called `$Math::Base85::base85_digits`,
which is a string containing the digits of the base 85 alphabet
from lowest (0) to highest (~), in that order.

Additionally, the following two functions are defined for general
use. (They will be exported upon request.)