An alternate base32 encoder (not RFC 3548 compliant).

The rationale for base-32 encoding in RFC 3548 [1] is as written therein: "The
Base 32 encoding is designed to represent arbitrary sequences of octets in a
form that needs to be case insensitive but need not be humanly readable.".

The rationale for our encoding is different -- it is to represent arbitrary
sequences of octets in a form that is as convenient as possible for human
users to manipulate.  In particular, z-base-32 was created in order to serve
the Mnet project [3], where 30-octet cryptographic values are encoded into
URIs for humans to manipulate.  Anticipated uses of these URIs include cut-
and-paste, text editing (e.g. in HTML files), manual transcription via a
keyboard, manual transcription via pen-and-paper, vocal transcription over
phone or radio, etc.

The desiderata for such an encoding are:

 * minimizing transcription errors -- e.g. the well-known problem of confusing
   `0' with `O'
 * embedding into other structures -- e.g. search engines, structured or
   marked-up text, file systems, command shells
 * brevity -- Shorter URLs are better than longer ones.
 * ergonomics -- Human users (especially non-technical ones) should find the
   URIs as easy and pleasant as possible.  The uglier the URI looks, the worse.