TensorFlow.NET 0.11.8.1

Changes since v0.10.0: 1. Upgrade NumSharp to v0.20.3. 2. Add DisposableObject class to manage object lifetime. 3. Add tf.no_op, tf.nn.in_top_k, tf.GraphKeys and tf.trainable_variables. 4. Change tensorflow to non-static class in order to execute some initialization process. 5. Overload session.run(), make syntax simpler. 6. Add Local Response Normalization. 7. Add tf.image related APIs. 8. Add tf.random_normal, tf.constant, tf.pad, tf.shape, tf.image.resize_nearest_neighbor. 9. MultiThread is safe. 10. Support n-dim indexing for tensor. 11. Add RegisterNoGradients 12. Add CumsumGrad, BroadcastToGrad. 13. Return VariableV1 instead of RefVariable. 14. Add Tensor overload to GradientDescentOptimizer.