Created by: JiayiFeng

This is only a draft of tensor implementation for review and it has not been fully tested.
So DO NOT MERGE THIS PR. Comments are welcome if you have any idea or suggestion for my code.

In addition, during my coding work I came up with several other questions that need to be discussed:

1. Do we need to rename functions from Majel (such as member functions of DDim and Place) to follow google c++ style?
2. In ported Majel code, we use glog to do asserting jobs, while in the other part of refactored Paddle we plan to use our own macro(paddle/platform/assert.h). Are we going to unify them?
3. Stride is removed in current tensor design. Is that going to be a problem?