*   Speed up matrix * vector multiplication and matrix * matrix with unknown
    shapes.
*   C API: Graph imports now support input remapping, control dependencies, and
    returning imported nodes (see `TF_GraphImportGraphDefWithReturnOutputs()`)
*   Multiple C++ API updates.
*   Multiple TensorBoard updates including:
    *   Users can now view image summaries at various sampled steps (instead of
        just the last step).