* Sketch of attribute walker

* Review comments

* merge error?

* Remove unused method

* simplify, make some ser tests work

* Don't look for keys that aren't there

* Factory registry, more ops visited, generic ser/dser start

* More merge

* cleanup

* Adapter for enums

* Compiler error

* Test of user-defined op

* Simplify enum name pairing

* Update distributed.hpp

* Review comments

* compiler error

* Direct access to non-primitive types from adapters

* Define and export type info

* attr enums, AvgPool*, vectors

* Cleanup

* some comments

* Allow type info to be used as a key.

* Don't leave output serialization shapes set.

* Auto adapter

* More ops, adapters

* Missing symbol

* Remove PartialShape and element::Type methods from visitor

* Fix type info

* Remove unused variable

* Simplify

* namespace error

* exports

* Uniform names

* Some better names

* More name cleanup, simplify visitor implementation

* Fix template, add test

* Revert serializer

* Add instantiations

* Work-around gcc issue

* VS exports

* VS exports

* windows export

* vs

* vs

* vs

* vs

* Simplify

* vs

* vs

* Add some missing attributes

* Missing factories

* Merge error

* Fix Add factories

* Missed type