Support fp16 data type for more operations and fix the minor errors.  (Don't use this! It's an incomplete version)

1. Use the _CheckData with tolerance in unit test to avoid the bug in "0.0F != -0.0F" case.
2, Clean the codes.

1. Support to copy parts of source tensor to parts of target tensor.
2. New unit test for CopyIndex function.

1. Move the New/Initial/Del Tensor functions from XTensor.* to XElement.*
2. Move IsSameShaped functions from XTensor.* to core/shape/IsSameShaped.*
3. Move CheckData functions from XTensor.* to core/utilities/CheckData.*

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. Bug fixed; 2. Support abs, sign, convert data type(float <->int) ;3. Merge with xu and xiao branch

1. Support check data with tolerance, get data from n dim with int format; 2. Bug fixed; 3. Format correction; 4. New tests