Feature Request: Sub-tasks support in Inline-Todo

[SeptemberHX]

For example:

- [ ] Parent Task 1
    - [ ] Sub Task 1
        - [ ] Sub Sub Task 1
        - [ ] Sub Sub Task 2
    - [ ] Sub Task 2

It should:

1. correctly recognize the parent-children relationship between tasks
2. allow to collapse/open task details, which includes the task description and more details about the sub tasks. Also show a nice progress bar when collapsed.
3. allow to show parent task for sub tasks and click to jump to the parent task in sidebar
4. auto mark parent tasks as complete when all sub tasks are finished