Towards support for int63 in the VM on 64-bits architectures.
Renamed Int31 to Int63.
More safety in conversion from Uint63.
Fix compilation of literals on arch64.
Fix bug for lsr and lsl. Due to usage of C macros with side effects in
variables...
Fix typos in print_instr.
Fix for lsl and lsr.
Fix for head0.
Rename INT31 instructions into INT63.
Fix tail0.
Fix mulc.
Fix addmuldiv.
Native div21 implementation (a bit naive for now).
Remove debug printing.
Implemented div21 for vm_compute.
Fix addmuldiv.
Fix div21 in test-suite.

All arithmetic tests are now successful on 64-bits architectures.
Heavy cleaning still to be done, though.
Fix after renaming to Int63.
Doc now mentions Resource.v.