[edk2-staging/BaseToolsOpt]: Add new branch BaseToolsOpt

["Gao, Liming" <liming.gao@intel.com>]

Hi All,
  I would like to add new branch BaseToolsOpt in edk2-staging for BaseTools build performance optimization. Here is its Readme.MD. Please help review.

Readme.MD:
This branch is used to optimize BaseTools build performance. It bases on edk2 repo UDK2017 branch.

The branch owner:
Gao, Liming <liming.gao@intel.com>
Zhu, Yonghong <yonghong.zhu@intel.com>

## Feature Introduction
BaseTools supports more and more features. They will take more build time. To reduce build overhead, some points have been 
identified to be optimized. POC code will be added in this branch for evaluation.
1) Enable the multiple thread in GenFds phase.
2) Support to merge multiple drivers into one. It should save the link time. But, it doesn't save much in the multiple build. 
   Besides, this feature can save the image size when the image is not compressed, such as PEI images.
3) Reduce the extra copy actions in build process.
4) Analyze cProfile data and enhance the parser logic. https://bugzilla.tianocore.org/show_bug.cgi?id=42

## Timeline
Target for 2017 Q3

### NOTES
Most changes in this branch are BaseTools. To apply them, user needs to run BaseTools 
from sources. In Linux, BaseTools run from source. In Windows, BaseTools can run from source. And, Reconfig option is also 
required to apply new config settings in BaseTools\Conf. The step is like below:
1. enter into edk2
2. set PYTHON_HOME=C:\Python27
3. type edksetup.bat --nt32 Reconfig
4. nmake -f BaseTools\Makefile
5. type build command to build platform.

Thanks
Liming