v0.1.7

Deprecated: --mining_sentence_size and --training_sentence_size. Load all sentences by default. --input_sentence_size can be specified to limit the sentences to be loaded
Feature: added --unk_piece/--bos_piece/--eos_piece/--pad_piece flags to change the surface representations of these special symbols.
Bug fix: added third_party directory for cmake's subdirectory.

For more detail:
v0.1.6...v0.1.7