Moving subheads and contents when archiving

[jgclark]

Need to make Archiving smart to move subheads and their contents as well - Or is the better archiving now introduced in v2.4.4 enough?

Some earlier jottings:

# Spec for subheads etc.
# Read all into a more detailed data structure and then write out?
#  - Title line
#  - 1 or 2 metadata lines, starting with #tag or Aim:
#  - open section
#    - (opt) Heading line
#      - (opt) Sub-heading
#        - (opt) Task
#        - indented lines of comment or bullet or just text
#  - done section ('#[#] Done') -- to include cancelled, unlike NP built-in behaviour
#    - as above