Resolve "32-bit ABC code"

Closes #88 (closed)

To do:

• Implement missing instructions
• Fix 64-bit version of get_double_real and store_double_real in the C target
• Fix printing of DREAL nodes on 64-bit platforms in debug_curses.c
• Wasm implementation
• Garbage collection for unboxed arrays of DREAL

For a moment it seemed that the Wasm implementation became up to twice slower (compare old vs new, both with 64-bit Clean, both on runner1), but this seems to be a CI artefact; compare these slow-downs compared to native Clean for 64-bit ABC code on WebAssembly mentioned in the IFL'19 paper, on the current master branch, and on this branch:

Benchmark	Paper	master	32-bit
brainfuck		11.0	11.1
fsieve	3.71	3.40	3.43
lqueen	9.5	7.72	7.66
nfib	13.3	13.4	13.1
parser		2.78	2.85
prolog		6.42	6.32
reverse	3.85	2.34	2.40
rfib		19.8	19.9
squeen		9.78	9.98
symsieve		5.62	5.57
tak	15.1	14.5	14.5