Add support for callouts with no header

[ShahriarKh]

Obsidian Admontion has the option to create callouts without a title. This pull-request adds support for it by giving the callout content a top border when callout title is empty.

[damiankorcz]

Hi @ShahriarKh, Can you give me an example of how to initiate this so I can test it? I've got Admonition Plugin installed and the code you provided. Is there a setting I have to turn on for this to work? I've created a Note callout with the following Markdown:

> [!note]
> This is an example of a Note Callout.

As you can see it's still rendering the default callout title.

[ShahriarKh]

Hello @damiankorcz! Try Admonititon syntax and leave the title empty:

```ad-note
title:
some text

https://github.com/valentine195/obsidian-admonition#title

[damiankorcz]

Hi @ShahriarKh, Ah I see. I've merged the change. Thanks!

[ShahriarKh]

👍🏽