experiment with air mines. thought they could make shoppa... interesting. ToDo: Allow mines to give up, tweak distances, real graphics, toggle for whether they can acquire a new target while they haven't given up.

void fpcrtl_halt(int num) {
    __coverity_panic__();
}

int fpcrtl_abs(int num) {
    return num >= 0 ? num : -num;
}