changed symbol table implementation
minor changes
changed language model and many minor changes
1. changed overall model
2. add preliminary supprot for multi-nonterminal
1. various subtle changes
2. can decode one sentence
1. support multi-thread translation
2. can replace moses-chart decoder
3. various changes
4. few bug fix
fix one bug in output_buffer, still need to test multi-threaded function
1. changed runtime output to stderr
2. reduce memory used by output_buffer
3. add mutex to language model