* First pass at Relay-to-Python converter testing utility

* Indicate astor as a dependency

* Add astor dep to host as well

* Typos and small bugs

* Handle ADTs and matching in Python conversion

* Remove any dependency on ast.parse

* Eliminate unnecessary type var field in Python version of ConstructorValue (already gone on C++ side)

* Update constructor value, fix syntax errors

* Don't forget keywords arg on Call nodes

* Fix some incorrect calls to ast nodes

* Fix more calls, a little more cleaning up

* Missing cases in attr conversion

* Lower op calls instead of running them through interpreter, as in @MarisaKirisame's AoT compiler

* We do still need the module

* Remove changes to op attrs: Will PR separately

* Smoke test and corrections

* More tests and fixes

* Ensure imports are properly global in generated Python code

* Add unit tests for refs

* Add unit test for tuple indexing

* Add unit test for if expression

* Remove astor dependency

* Remove astor from meta.yaml too

* Fix if test and add basic local function test

* Add global function test, refactor earlier tests

* Correct 'clause' field in ADT so Python and C++ field names match

* More fixes and tests for matching and constructors

* Dramatically simplify matching: no need for a thunk

* Improve ref writing test

* Ensure local recursion works

* cleanup

* Add test for global recursion

* Add test for higher-order calls

* Get ops working, add basic tests

* Remove accidentally duplicated test

* More docstrings to appease pylint

* Forgot to fix a test using constructor values

* Reduce optimization level in fusion and fix tuple input to operators

* Test op with tuple output, fix tuple output code

* Add unit test for batch norm

* Add a couple more tricky test cases

* Correct nat constructor to drop unnecessary field

* Fix the op attrs file (accidentally reduced it)

* Address review comments

* Adapt to new ConstructorValue representation (no more runtime dep on module)

* Use pass manager and updated interfaces. Extend module.from_expr to accommodate necessary demands

* Use sequential return value

* Lift out nested conditionals

* Replace triple single quotes with triple double quotes

* Use main variable instead of entry_func