Merge pull request #257 from shark8me/save-gradients-flag

support for turning on gradient outputs in :compute-graph's :buffers for debugging

Merge pull request #256 from thinktopic/tensor-losses

Removed the majority of the complexity of the math subsystem

Started removing functionality.

Updating center-loss to use a hypersphere for placing centers

starting to add radius to center-loss.

Merge pull request #253 from iboss-ptk/master

Update brew cuda installation instruction

Merge pull request #251 from shark8me/experiment-classification-api

Merge pull request #249 from gigasquid/remove-first-dropout-from-mnist-example

Merge pull request #247 from gigasquid/selu-activation-and-tensor-operations

metrics for train and test loss via the experiment API

Updated centerloss test and fixed centerloss.

Trying to get the last loss, center-loss ported over.