v1.4.0

• Add different environment.yml files for easy installation using conda. You can now
  create a ready-to-use conda environment by just calling conda env create -f environment-cuda<VER>.yml.
• Make NumpyDataset memory efficient by keeping float16 arrays as they are
  until batch creation time.
• Rename Multi30kRawDataset to Multi30kDataset which now supports both
  raw image files and pre-extracted visual features file stored as .npy.
• Add CNN feature extraction script under scripts/.
• Add doubly stochastic attention to ShowAttendAndTell and multimodal NMT.
• New model MNMTDecinit to initialize decoder with auxiliary features.
• New model AMNMTFeatures which is the attentive MMT but with features file
  instead of end-to-end feature extraction which was memory hungry.