nnet3: various changes relating to ctc training

src/bin/acc-tree-stats.cc

src/bin/sum-tree-stats.cc

src/ctc/cctc-training.h

src/ctc/ctc-supervision.cc

src/ctc/ctc-supervision.h

src/kws/kws-functions.cc

src/nnet2bin/nnet-relabel-egs.cc

src/nnet3/Makefile

src/nnet3/nnet-compile-utils.cc

src/nnet3/nnet-ctc-example.h

src/nnet3/nnet-example.cc

src/nnet3/nnet-example.h

src/tree/build-tree-utils.cc

src/util/kaldi-table.cc

src/util/text-utils.cc