Make ASDL parsing, loading and traversing more flexible
Add some things to ASDL schema parsing
Add preliminary AST node generation from ASDL
Better Python AST node code generation
Generate simple pxd overlays for generated AST nodes
Test ASDL generated nodes
Generate string representation functions
Generate visitors and transformers
Improve and test generated visitors and transformers
Add package building and feature selection
Make optional compilation work
Test package building
Add test for issue #204
Simplify and cleanup previous commit.
Simplify some things
Fix premature module verification problem (Issue #204)
Fix some ASDL builtin types
Add grammer for normalized IR and build script
Add ASDL schema for untyped IR
Verify schema for python keywords