[crossfire] Plugin system

[Nicolas Weeger]

Hello.

I plan on rewriting part of the plugin system (after the incoming
release, of course!).

Here's what I'll do:
* create a libplugin (or whatever) that contains wrappers for all
functions plugins will be able to call. Basically one .c file that
you'll link to your plugin. Remember that under Windows you *can't* link
directly to libcross and hope it works from there, thus need wrappers
for *all* functions that use malloc/free/variables initialized in server.
* create a small Perl script to generate those wrappers directly from
the Crossfire sources, probably based on a wanted function list. Will
not be hard, and will make adding functions much easier. Could generate
plugins.c file too (or at least the server-side wrappers, put in another
file).
* ensure the 3 existing plugins compile correctly under Windows :)

Suggestions, comments & flames welcome, as usual ^_-

Ryo