*   Shape strictness: all fed values must have a shape that is compatible with
    the tensor they are replacing
*   Exposed `tf.while_loop` (deprecated `control_flow_ops.While`)
*   run() now takes RunOptions and RunMetadata, which enable timing stats
*   Fixed lots of potential overflow problems in op kernels
*   Various performance improvements, especially for RNNs and convolutions
*   Many bugfixes