This PR adds the underlying utilities for much faster nnet3 inference on GPU, and a command-line binary (and script support) for nnet3 decoding and posterior computation.  TBD: a binary for x-vector computation.  This PR also contains unrelated decoder speedups (skipping range checks for transition ids... this may cause segfaults when graphs are mismatched).

…th recent versions (#2760)

…data.sh (#2762)

…r small fixes. (#2768)

#2771)

…ults (#2775)

Phonetisaurus is much faster to train then sequitur.

…ion (#2716)

…2776)

…2792)

…(for e2e) (#2779)