Toggle headlines

[jgollenz]

fixes #164

todo:

• toggle top level headlines (bug)
• toggle plain list items
• toggle first line of paragraph (bug)
• add tests
• toggle checkboxes to TODO headlines/DOCS.md#org_indent_mode)
• add docs

[levouh]

Don't forget to run make format as well.

[jgollenz]

@kristijanhusak the orgmode docs talk about "regions" that can be toggled as a whole. I don't use Emacs, do you know what is meant by this term? Is this something that's already used by nvim-orgmode?

[jgollenz]

@kristijanhusak I'd need your opinion regarding the visual-mode mappings I mentioned in #164 (bottom) to move on with this PR ;)

[jgollenz]

@kristijanhusak one last thing: I cannot detect a line that has no parent-headline with get_closest_headline(), because it will throw an error. I hacked this together:

function Files.has_headline(id)
  local current_file = Files.get_current_file()
  local msg = 'Make sure there are no errors in the document'
  if not vim.diagnostic then
    msg = string.format('%s by running :OrgDiagnostics command', msg)
  end
  if not current_file then
    error({ message = string.format('Failed to parse current file. %s.', msg) })
  end
  if not current_file:get_closest_headline(id) then
    return false
  else
    return true
  end
end

But it introduces some code duplication and I hate that. Do you have a better idea for how to check if a line even has a headline?

[kristijanhusak]

@jgollenz I pushed small change where get_closest_headline() should return nil instead of throwing an error. Rebase and give it a try.

[jgollenz]

@kristijanhusak works like a charm, thanks! You prefer squashing commits, right?

[kristijanhusak]

@jgollenz Yeah, squashed commit is perfect.
I gave this a test, works great! Thanks!