Support reserved property in XTensor to indicate whether the data is reserved for backward.

Merge with the branch of xuchen (NOT update the float16, this needs code review) and fix the bugs in Gather function.
1. Support Reciprocal fucntion.
2. Fix the safe delete bugs in XDevice.
3. Support new API to convert the data type of tensor.
4. Support to show the memory usage of buffer memory.
5. Fix 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. 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 SetAscendingOrder functions from XTensor.*  to core/utilities/SetAscendingOder.*
2. Rename XElement.* files to XCall.*

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.*

2. fix the bug of onehotandindex
3. modify the data initilization of transformer
4. add the DumpFormat (need reimplement)

1. Merge with Huchi branch (replace all requireLink with enableGrad that allows gradient computation for a tensor);
2. Update the global memory size (This may make the memory size a little bit larger than the old version).

2. Add MemManager class to manage the memory;
3. Use the new version XList;
4. Add a new interface to create Tensor;
5. Apply MemManager to FNNLM.