Add support for underline style headings

[wilbowma]

Fixes #72

Comes with lots of options:

The defaults retain the old behaviour.

This is my first TypeScript in a while and my first Obsidian plugin so let me know if I did something stupid.

[dvcrn]

wow that was quick! Thanks a lot for the PR, let me try to get this reviewed today

[wilbowma]

Had an hour to spare and your code was easy to follow :)

[dvcrn]

The format is currently breaking, could you run yarn format to apply the prettier presets to all files?

[wilbowma]

Fixed

[dvcrn]

When changing underline string from === to something else, and 'replace heading style' is enabled, should this replace === to the new string?

My assumption without reading the code was that it will force the heading style to be whatever is set in the settings, but currently it doesn't change the underline

[dvcrn]

Left a few small comments, besides that it looks good to me 👍

[wilbowma]

Think I fixed them all.

[dvcrn]

Tested and working great! I'll go ahead and merge this

There's still the comment regarding fileLines[i + 1].match(/^=+$/) !== null. I have a feeling this breaks when the underline is set to something else than =. Maybe not the original intent of this PR for someone to use ___ for example, but since it's possible I reckon people will do that

[dvcrn]

Released in https://github.com/dvcrn/obsidian-filename-heading-sync/releases/tag/1.9.0

[wilbowma]

If someone uses ___ as the underline, that's not a Heading 1 by the markdown spec, so it shouldn't be read as the heading.

It might be worth adding some validation to the settings to ensure only a sequence of =s is used.