Phrase support based on word2phrase

First approach to learning phrases based on wordphrases. Please comment. Not test and proper documentation yet. But they will come. 
Yeah I was thinking something similar same. Word2phrase avoid this by pruning not by 0.7 but slowly increasing a minimum threshold (`min_reduce`) starting at 1. I.e. once reached 0.7 * max_vocab_size for the first time it will remove every word with count of 1, the second time everyword with a count less than or equal than 2 and so on (this is the way it was implemented before, should I go back to something similar?).