refactor: use debug_helper #414

Context

As v8 API evolves and changes, we have to catch and handle breaking changes in the code.

@kvakil suggest to use debug_helper in llnode see proposal.

The debug module includes GetStackFrame and
GetObjectProperties functions. Presumably, V8 would be receptive to
patches to implement other functionality.

Scope

The main goal is to make llnode more maintainable in the mid/long term.

• Reducing llnode's dependency with v8 API breaking changes
• Documenting how to maintain debug_helper dependencies
• Having a proper testing strategy

Risks/Questions

• List what is missing in debug_helper that we need in llnode
• Estimate the amount of work to do in debug_helper
• How to include debug_helper into llnode (as a dependency)