1. fixed the bug in the Spread function.  2. add compare and OnehotAndIndex function 3. optimize the code

1. add gather function 2. add cross entropy forward computation and backward computation 3. code optimization 4. merge with xiaotong-working branch

1. add dropout function 2. add some function in tensor/core/math/unary file 3. merge with xiaotong-working branch

1. add macro to implement unary function 2. add sub and div function 3. merge code with the latest branch of xiaotong-working