- HDoParseRetBreakpoint wasn't calling top_level_parse.return_from_h_do_parse()
- Fixed KeyError in return_from_h_do_parse()
- Print parser stack and input preview after apply, as with hammer-parse-step

- ASTManager helper class to hold the top node of the ast to be printed
- HDoParseRetBreakpoint
- ast printing commands
- Update BreakpointManager tests with HDoParseRetBreakpoint tests
- Add support in TopLevelParse to select a stack item for printing the AST node of