Init time option lstm_num_threads should be used to set the number of LSTM threads

Changed the WERD_RES linked link to use shared pointers instead of raw pointers.
This is needed so that even if one thread deletes a WERD_RES object, other thread's which needs to iterate thru them can still access it safely.
In terms of LSTM processing, only one threads processes one WERD_RES. This change is needed as all the threads can iterate thru due to single linked list data structure.