* support sentencepiece for bertjapanesetokenizer
* add test vocab file for sentencepiece, bertjapanesetokenizer
* make BasicTokenizer be identical to transformers.models.bert.tokenization_bert.BasicTokenizer
* fix missing of \n in comment
* fix init argument missing in tests
* make spm_file be optional, exclude spiece.model from tests/fixtures, and add description comments
* make comment length less than 119
* apply doc style check
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