added deterministic vectors

Added option for deterministic initial vectors

Gensim already had the ability to precisely reproduce a model by using the
same seed when training on the exact same corpus.  The array syn0[] will
always have the same vector at each index.  However, models trained on
separate corpora or even slightly different corpora may have
different vocabs in different orders.  I add an option to use
"deterministic" initial vectors to link the seeding for the creation of
each vector directly to the corresponding word via hashing.  I also
concatenate onto the word the seed specified in the arguments so that a
user can tinker with different deterministic initial vectors with
reproducible results.