typo

* add unit test for serializer and complete new interface for hdf5
files

* test both versions msgpack and pyarrow

* use np.asarray

* changes from review

* update

* Change VGG19 example to tf.layers.

As part of the transition towards tf.layers #291, #627 this is a
rewrite. While The LinearWrap might need less lines, tf.layers are
supported by TensorFlow. And the motivation of tensorpack is being
a training framework.

* cosmetic changes