why:
subsequent development will compile sources as main without setting
the vm2_enabled flag. also, the doc generator would fail an vm2 without
setting the flag for the vm2 files.
why:
these files provide part of the externally accessible interface
provided by vm_cpmputation.nim, vm_internals.nim. so the
new filename indicates that the source code belongs to vm2 (rather
than vm).
why:
these files provide part of the externally accessible interface
provided by vm_state*.nim. so the new filename indicates that the
source code belongs to vm2 (rather than vm).