remove Cons instruction, rename Cons2 to Cons

(compiler proofs not updated)
update compiler implementation for Cons removal
update proofs up to prim1_to_bc_thm
update proofs about consing closures
update compiler proof
add back old (swapped) version of zHEAP_EL

just for use as a macro in other instructions. the real El(2)
instruction still gets the new version.
partial progress on zHEAP_DEREF

got stuck because x64_payload_def is wrong (and possibly other
problems...)
some work on the new Cons(2) implementation
fix zHEAP_DEREF
fix Deref case of zBC_HEAP_THM

also, cheat/fixup some places where the changed type of Cons causes errors
delete unmatched end-comment token
failed attempt to prove zHEAP_UPDATE_REF
hack on zHEAP_UPDATE_REF

not obviously making progress
add missing open lcsymtacs for ml_heapScript.sml
more hacking on zHEAP_UPDATE_REF

it's down to something about one_list changing due to a memory update,
which I don't really understand...
prove zHEAP_UPDATE_REF

not sure it's right though: haven't updated the bytecode simulation
theoerm yet.
update Update case of zBC_HEAP_THM
attempt to add byte arrays to ml_heapTheory

got it to build, but might be totally wrong.
fix Bytes_def and x64_payload_def for wide refs
fix zHEAP_isBlock