Question answering on the Facebook bAbi dataset using RNN

Minor note for anyone wanting to re-run all the experiments, there's a one line change that needs to be done such that it will run on QA19[1]. I'll be pushing the updated code to Keras mainline soon.

Otherwise, all experiments run out of the box, with many of the experiments doing the full training and testing in under a minute. Play around! :)

[1] https://github.com/Smerity/keras/commit/63284a47ffc83e485500...