* a complete, roud-trippable Krnl dialect operation definition
* remove old dialect definition files, edit build files
* register dialect
* check in src for onnf_opt and dimension handler types
* re-trigger jenkins
* fix build
* clarify operation semantics
* add verifier for krnl.iterate
* refactor to make things clear
* do not hard code types
* nit and add comments
* fix rebase
* update op implementation
* fix merge
* update kernel dialect definition
* more comment on how to use the builder for krnl.iterate operation
* ammend the comment
* can parse krnl.iterate
* can parse and print if bounds are not SSA values
* address comments
* better error handling
* Update CMakeLists.txt
* update comment
* reflow comments
Tian Jin