Simple GEM Window Based Drawing Demo

 * "demo" : simple GEM window based drawing demo
 * Written by Eric R. Smith and placed in the public domain
 *
 * compile with: gcc -o demo.prg -O -mshort demo.c -lgem16
 * Should probably compile with other ST compilers, too. Note that
 * prototypes aren't used, so it doesn't require an ANSI C compiler.
 * Pure C will probably issue a lot of warnings because of this.
 */