define AlexNet architecture

Swap order of lrn and max pooling layers to reflect Krizhevsky
architecture. Initialize biases to 0.1 where Krizhevsky had 1, as
training by initialization with 1 has flat loss.
Document AlexNet model, include download script
include pretrained snapshot and performance details
Merge pull request #327 from shelhamer/alexnet

Include Caffe model for Krizhevsky architecture (AlexNet)