Czar's way to customize xwem-time

[Wassily Kondratiev <wk@xxxxxxxxxxx>]

Hi!

Let's imagine someone wants to change time digits. But they are constant 
objects,
so he should rewrite xwem-time.el file in its entirety and maintain all future
changes. I'm sure there is an easier way.

Btw, several time icons are defined as defvar (xwem-time-xpm-empty-digit,
xwem-time-xpm-time0, xwem-time-xpm-time1), but others as defconstant.
What deep sense it has?

wk.