* default cmvn compute config; more log of grad clip; diff ds2 cmvn compute and conf; ds2 lr step by epoch;

* fix ds2 config

* fix install and egs link

* sox speed pertrub shape (T, C), float64, process using int32

* fix libri ds2 scripts; add ngram and spm doc

* aishell ds2 cer7.86

* fix ds2 result