* Improve TypeId:
- move it to c10 namespace to allow for easy extraction from caffe2 into c10 (i.e. reuseability from aten)
- Use unordered_map/unordered_set instead of map/set for performance
- Make TypeId a type safe class (i.e. no implicit casts from/to int)
- Make TypeId constexpr
- Some readability improvements (e.g. using instead of typedef)
- Don't explicitly implement TypeMeta copy assignment and construction - let the compiler do that for us.
- Add TypeMeta move constructor
- Make TypeMeta members noexcept
- Implement TypeMeta::operator== and operator!= as free functions instead of in-class
* CR comments
* fix
* fix windows
* Rename back to CaffeTypeId
* Remove c10::TypeId/TypeMeta
* remove C10_KNOWN_TYPE
* code review
Summary: Adding support for DLPack tensors to Python op
Reviewed By: Yangqing
Differential Revision: D6577702
fbshipit-source-id: e14ef213fcdb2930ffe164667971a92aa8db503c
