This commit updates the stumpwm to version 0.9.8. Futhermore, it
refactors the expression quite a lot:
* stumpwm has been moved from lisp modules to window-managers.
* stumpwm has been added to the window managers NixOS knows about, this
enables the user to add stumpwm as a default window manager in his
NixOS configuration like with Xmonad or i3.
* the package has been split into stumpwm and stumpwmContrib. This is
due to the fact that development of stumpwm and its extension modules
has been split into two repositories. As of today, the release is the
last one before this split. This split into two packages only reflect
those upcoming upstream changes already.
It is planned to make the addition of the extension modules voluntarily,
like with Xmonads option "enableContribAndExtras". Furthermore it might
be possible to add an option to compile stumpwm with clisp instead of
sbcl.
