How to make a core ?
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* Download:
    ~ qemu
    ~ cpio
    ~ advcomp for advdef tool
        --> http://www.phpied.com/install-png-tools-on-mac/
    ~ the core (need to change cause of versioning...)
        --> see Flihabi/kernel repository

* The core:
$ make unpack
--> Change whatever you want in core/core-root
$ make pack
$ make test