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

1. Initialize and new scalar tensor.
2. Get and set scalar tensor.
3. Add ReduceSum test on scalar tensor.
4. Little bugs fixed.

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