Drop Python 2.7 support for Theano.

Merge pull request #62 from MarcBS/merge_upstream

Merge upstream

Fix tests

Update update_apy.py

Stable version 16th April 2018 minor edit

Fixes for *HD optimizers

New parameter in Concatenate layer (cropping for each input axis)

Fixbug MultiHeadAttention layer

Allow arbitrary input length in RNNs (TF backend)

Added required endline