PReLU Layer and its tests

PReLU Layer and its tests

described in Kaiming He et al, "Delving Deep into Rectifiers: Surpassing
Human-Level Performance on ImageNet Classification", arxiv 2015.

Belows are commit message histories that I had while developing.

PReLULayer takes FillerParameter for init

PReLU testing consistency with ReLU

Fix : PReLU test concistency check

PReLU tests in-place computation, and it failed in GPU

Fix: PReLU in-place backward in GPU

PReLULayer called an incorrect API for copying
data (caffe_gpu_memcpy). First argment of `caffe_gpu_memcpy` should be
size of memory region in byte. I modified to use `caffe_copy` function.

Fix: style errors

Fix: number of axes of input blob must be >= 2

Use 1D blob, zero-D blob.

Rename: hw -> dim