float splits.
    *   `Conv2D`, `Conv2DBackpropInput`, `Conv2DBackpropFilter` now supports
        arbitrary dilations with GPU and cuDNNv6 support.
    *   `Estimator` now supports `Dataset`: `input_fn` can return a `Dataset`
        instead of `Tensor`s.
    *   Add `RevBlock`, a memory-efficient implementation of reversible residual
        layers.
    *   Reduce BFCAllocator internal fragmentation.