Minor change to behavior of :ObsidianNew command

[epwalsh]

Fixes #184.

The argument to the :ObsidianNew command can now be in one of 3 different forms which determine the behavior of the command:

1. A raw title without any path components, e.g. :ObsidianNew Foo. In this case the command will pass the title to the note_id_func and put the note in the default location.
2. A title prefixed by a path component, e.g. :ObsidianNew notes/Foo. In this case the command will pass the title "Foo" to the note_id_func and put the note in the directory of the path prefix "notes/".
3. An exact path, e.g. :ObsidianNew notes/foo.md. In this case the command will put the new note at the path given and the title will be inferred from the filename ("foo").

[peeeyow]

@epwalsh
Thanks for this feature. I have the tested it using the following config and inputs. Please verify if these are the intended behaviour.

require("obsidian").setup({
    -- other fields ...
    notes_subdir="",
    note_id_func = function(title)
      local suffix = ""
      if title ~= nil then
        suffix = title:gsub(" ", "-"):gsub("[^A-Za-z0-9-]", ""):lower()
      else
        for _ = 1, 4 do
          suffix = suffix .. string.char(math.random(65, 90))
        end
      end
      return tostring(os.date "%Y%m%d%H%M%S") .. "-" .. suffix
    end,
})

Path-like arguments

input	output file
dailies/new note	dailies/20230908073035-new-note.md
dailies/new;note ;	dailies/20230908073035-newnote--.md
dailies/	dailies/20230908073035-.md
dailies/	dailies/20230908073035-----.md
dailies/new note.md	dailies/new-note.md
dailies/new;note ;.md	dailies/new;note ;.md
dailies/.md	dailies/.md
dailies/ .md	dailies/ .md

Filename only arguments

input	output file
new note	20230908073035-new-note.md
new;note ;	20230908073035-newnote--.md
``	20230908073035-NHQQ.md
	20230908073035-NHQQ.md
new note.md	new-note.md
new;note ;.md	new;note ;.md
.md	.md
.md	.md

Noticeable difference between path-like and non path-like arguments

For arguments with empty title (either blank or white spaces only) without suffix .md:

input	title passed on note_id_func
dailies/	"" (empty string)
dailies/	" " (string field with spaces)
``	nil
	nil

For arguments with empty title (either blank or white spaces only) with suffix .md:

input	output file
dailies/.md	dailies/.md
dailies/ .md	dailies/ .md (spaces are preserved)
.md	.md
.md	.md (spaces are striped)

I believe this is already great. Thank you very much.

[epwalsh]

Thanks for the thorough testing @peeeyow! I've added some tests and better handling of these edge cases. 747d8ae