fix code style

Implement GPU kernel for cross entropy operator.

1. finish lookup table CPU and GPU kernel
2. Add some cuda helper
3. Add some math funtor

Rename `Net::AddOp` to `Net::AppendOp`

refine random related operators

* fix remote large update core

* wip

* working version

* fix style check

* fix style check

* update style check

Allow boot_bias for recurrent group to be static

Fix rowwise add

Add ScaleShiftLayer

Change class to struct in GemmFunctor to avoid errors on special compilers

Tune relative precision for unit test img_conv2 in test_NetworkCompare.

Use EigenBlasGemm improve convolution computing performance in ARMv7 environment.

  1. It's no problem with relative precision 1e-3 when testing several times in my local machine.
  2. But the testing failed with 1e-2 in the TeamCity, and only one value's relative precision is over 1e-2. So tune it to 4e-2

Fix #3582

Set the default cuDNN installation path