move binary-to-object to new tree structure
move codegen headers to include/
move abort.h to include, add namespacing
move runtime-array to include
move math functions out of common.h, and into include/avian/util/math.h
move heap.h to include
fix bootimage build
find headers regardless of directory layout in vm-depends definition
modify (THREAD_)RUNTIME_ARRAY definition so RUNTIME_ARRAY_BODY must be used

Previously, if you forgot to use RUNTIME_ARRAY_BODY to reference an
array declared with (THREAD_)RUNTIME_ARRAY, you wouldn't get a
compiler error until you tried to build on e.g. MSVC, where
runtime-sized stack arrays aren't supported.  This change ensures you
find out regardless of what compiler you're using, which ought to
protect us from regressions going forward.