Support injection of external state in TreeLSTM
Support injection of external state in TreeLSTM

Inject the hidden state of the tracking unit into the hidden state of the composition unit. This is only done when both units are using LSTMs.

stanfordnlp/spinn,nyu-mll/spinn,stanfordnlp/spinn,nyu-mll/spinn,nyu-mll/spinn,stanfordnlp/spinn