src/td.in: Add optimal_line_for_type()

Use the new function in insert_at_line():  whenever a given line $N is
equal to 0, meaning it doesn't exist yet in the file, the
optimal_line_for_type() will scan the file and answer with the "optimal"
line number that the the type should be inserted at.  It does that by
looking at the order in which types apper in $TD_TYPES, and compare that
with $TD_FILE:

- if a previous type has appeared already, it continues scanning the
  file until a different level 1 heading appears, or until the end of
  the file;
- if a type that comes after appears, it gets inserted before it;
- if no types exist in the file yet, it gets inserted at the end.

It fixes #td-05580844-40db-0db6-b11e-9f041a08c0a7.

0 files changed, 0 insertions, 0 deletions