better packaging - ship as a module, not a theme

i propose to package this as a module instead of a theme. this will reduce the number of steps to install, and let us keep more files within the module package instead of copying around. this makes for easier updating.

so, the proposal is to
- move this project to contrib/modules in cvs. optionally tell derek so he keeps commit histor. make sure this drupal.org project points top the new tarball.
- output flatforum.css like usual for modules. no need to copy
- include phptemplate_variables() in our own code and tell people to move it if they have a function conflict. one less file to move around and merge
- change readme so the only file that needs to move is node-forum.tpl.php. one day, theme engine might be smart enough to not require this.

i volunteer to add this to cvs if i can get some agreement from maintainer.