Neural turing machine implementation

Source http://arxiv.org/pdf/1410.5401v1

RMSprop http://arxiv.org/pdf/1308.0850v5.pdf - page 23

New implementation is highly inspired by Fumin Wang (https://github.com/fumin/ntm).