Add __builtin_popcount* based fast Hamming distance math function
Add and test sum of absolute values math functions for CPU and GPU
Add and test element wise sign math funtions for CPU and GPU
Instantiate caffe_cpu_sign for float and double
Add and test element wise abs math functions for CPU and GPU
Use macro to simplify element wise cpu math functions
Add and test non-in-place scale math functions for CPU and GPU
Add signbit math func, simplify GPU defs & instantiations with a macro
Merge pull request #159 from kloudkl/math_functions

Add more convenience math functions: hamming distance, sum of absolute values, elementwise sign and abs, and non-in-place scaling.