Trains a sentiment model.
The -trainPath argument points to a labeled sentiment treebank.
The trees in this data will be used to train the model parameters (also to seed the model vocabulary).
The -devPath argument points to a second labeled sentiment treebank.
The trees in this data will be used to periodically evaluate the performance of the model.
We won't train on this data; it will only be used to test how well the model generalizes to unseen data.
The -model argument specifies where to save the learned sentiment model.