1. Try to fix the bugs in destroy the stream of XDevice (Uncheck).
2. Fix the bug of memory leak in ReduceSumAll function.
2. Adjust the directory structure.
3. Fix the minor errors.

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

1. Supporting efficient propagate and gradient accumulation for backward functions.
2. Update the setData functions.
3. Clean the codes.

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. 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