BaseTools: Add PackageDocumentTools into Scripts folder

This tool is used to generate the document for edk2 packages. The
generated document will be in UDK release. For example, UDK2017
document can be found in:
https://github.com/tianocore/tianocore.github.io/wiki/UDK2017#documentation

Cc: Star Zeng <star.zeng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>