why3

See #151.
At the moment, this transformation is only integrated into TryWhy3,
in order to restore left-hand side splitting under vc:sp.

I suggest to integrate "generalize" into split_vc unconditionally.
I've tested that, the sessions were only broken for 4 examples:
  examples/tortoise_and_hare/
  examples/verifythis_2018_array_based_queuing_lock_2/
  examples/verifythis_2018_mind_the_gap_2/
  examples/multiprecision/toom/