* [NODE][REFACTOR] Refactor reflection system in node.

- Removed the old Node, Node is now just an alias of runtime::Object
- Introduce ReflectionVTable, a new columnar dispatcher to support reflection
  - This allows us to remove vtable from most node objects
  - The VisitAttrs are registered via TVM_RESGITER_NODE_TYPE,
    they are no longer virtual.
- Consolidated serialization and reflection features into node.

* Explicit type qualification when calling destructor.

* Fix SPIRV, more comments

* [REFACTOR][NODE][RUNTIME] Move Node to the new Object protocol.

This PR removes the original node system, and make node as a subclass of Object.
This is a major refactor towards a better unified runtime object system.

List of changes in the refactor:

- We now hide data_ field, use Downcast explicitly to get a sub-class object.
- Removed the node system FFI in python.
- Removed the node C API, instead use PackedFunc for list and get attrs.
- Change relay::Op::set_attr_type_key(attr_key_name) to relay::Op::set_attr_type<AttrType>().
  - This change was necessary because of the new Object registration mechanism.
  - Subsequent changes to the op registrations
  - The change revealed a few previous problems that is now fixed.
- Patched up a few missing node type registration.
  - Now we will raise an error if we register object that is not registered.
- The original node.h and container.h are kept in the same location.
- Calling convention: kObjectHandle now equals the old kNodeHandle, kNodeHandle is removed.
- IRFunctor now dispatches on ObjectRef.
- Update to the new type checking API: is_type, derived_from are replaced by IsInstance.
- Removed .hash member function, instead use C++ convention hasher functors.

* Address review comments

* [Codegen] Support broadcast op with symbolic shape

* fix case where last dim = 1

* use enum; simplify stride calculation; improve doc

* fix lint

* improve py doc

* [HEADER] ASF header dir=include

* [HEADER] ASF Header dir=src

* [HEADER] ASF Header -dir=python

* [HEADER] ASF header dir=topi

* [HEADER] ASF Header dir=nnvm

* [HEADER] ASF Header -dir=tutorials

* [HEADER] ASF Header dir=tests

* [HEADER] ASF Header -dir=docker

* fix whitespace

* [HEADER] ASF Header -dir=jvm

* [HEADER] ASF Header -dir=web

* [HEADER] ASF Header --dir=apps

* [HEADER] ASF Header --dir=vta

* [HEADER] ASF Header -dir=go

* temp

* [HEADER] ASF Header --dir=rust

* [HEADER] Add ASF Header --dir=cmake

* [HEADER] ASF Header --dir=docs

* [HEADER] Header for Jenkinsfile

* [HEADER] ASF Header to toml and md

* [HEADER] ASF Header to gradle

* Finalize rat cleanup

* Fix permission

* Fix java test

* temporary remove nnvm onnx test

* when there is no intrin func, using body for initialization. For issue 714.

* Refine code per review comments, and add a test case.

* Fix lint issues.

* Re-organize the tensorize test cases, and add a new case for none-reset
mode.

* Fix a typo.

* Delete the unit case because merged it into test_schedule_tensorize.py already.

* always use new tensor in its stage when rewrite for cache read

* revert previous changes to sync up with master

* support using the ptr with an original offset

* update test case and fix CI error

* Support rank-0 tensor

* fix lint

* Support vector operations for AMD (llvm IR)

* fix whitespace

* update comments, docstring

* [PASS] copy intrin

* update comment thanks to derisavi

* [RUNTIME][PASS] Allow declare vector type array

* fix bcast

* [BUFFER] Enable vload/store function in buffer

* ok

* [STORAGE][BUFFER] Support access ptr for clear access pattern.

* fix lint

* [IR] Add body to AssertStmt

* fix lint

* [RUNTIME] Refactor runtime to be DLPack compatible. Enable plugin of new runtime.

* fix mac compile

* ok

* [LLVM] Initial support for codegen LLVM.

* Fix the naming issue of codegen

[TEST/PYTHON] Add unittest folder, add a build pipeline. Rename Buffer.ptr to Buffer.data to be consistent with Array. (#29)

* [CODEGEN] Add LoweredFunc, MakeAPI and SplitHostDevice

* update halideir

* [LANG] Include buffer semnatics, introduce pylint

* Refactor inline add support for buffer indexing

* fix doc