Stable ABI

Across all architectures, some offset are referred to by off-
sets that don't change (well, not without some binary manipu-
lation). Here's the complete list of these references:

04 BOOT addr         06 (uflw) addr      08 LATEST
13 (oflw) addr       2b (s) wordref      33 2>R wordref
42 EXIT wordref      53 (br) wordref     67 (?br) wordref
80 (loop) wordref    bf (n) wordref

BOOT, (uflw) and (oflw) exist because they are referred to
before those words are defined (in core words). LATEST is a
critical part of the initialization sequence.

                                                        (cont.)