depth of section parsing

[nextuponstream]

• Parse a section that is 3, 4, 5... level of heading
  Currently only 3
• Select a subsection within a subsection
  given

# Title

## Task list

### Not interesting section

#### Subsection

* [ ] don't parse this

### Section

#### Subsection

* [ ] do parse this

then

todo list -t title -so --section Section --subsection Subsection
Todo lists from /home/path/to/todos/category
# task-list
## Section
### Subsection
* [ ] do parse this