Parallel softmax.

Parallelized the softmax layer using the reduce algorithm.
For the nnjm application, this is needed due to the large
size of the output layer.
Hacky change that will work only in one dimension.
added some explanations for modifs on softmax

-- underflow/overflow
-- 2 kernel calls hard coded explained
-- identity elt explained
-- removed useless syncthreads
Merge pull request #1 from jmp84/speedupSoftmax

Parallel softmax.