Created by: iclementine
- fix a bug in RNN(that it does not initialize the state for the cell correctly). The code to generate default initial state for a cell wrapped in an RNN is moved to
- BiRNN now does not reuse the initial state for forward & backward initial states. It must be a 2-tuple of cell states, or None;
- add testcases of RNN & BiRNN;
- update unittests for static graph by using
- fix typos in docstrings.